28354: Difference between revisions
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'''28354 (Florin Bojor)''' | '''28354 (Florin Bojor)''' | ||
''Fie <math>O</math> punctul de intersecție a diagonalelor patrulaterului convex <math>ABCD</math> și punctele <math>E</math> ,<math>F</math> ,<math>G</math> și <math>H</math> pe segmentele <math>OA</math>, <math>OB</math>, <math>OC</math>, respectiv <math>OD</math>, astfel încât <math>AE = BF = CG = DH</math>. Notăm cu <math>I</math>,<math>J</math>,<math>K</math> și <math>L</math> mijloacele segmentelor <math>AB</math>, <math>BC</math>, <math>CD</math>, respectiv <math>DA</math> și cu <math>M</math>,<math>N</math>,<math>P</math> și <math>Q</math> mijloacele segmentelor <math>EF</math>, <math>FG</math>, | ''Fie <math>O</math> punctul de intersecție a diagonalelor patrulaterului convex <math>ABCD</math> și punctele <math>E</math> ,<math>F</math> ,<math>G</math> și <math>H</math> situate pe segmentele <math>OA</math>, <math>OB</math>, <math>OC</math>, respectiv <math>OD</math>, astfel încât <math>AE = BF = CG = DH</math>. Notăm cu <math>I</math>,<math>J</math>,<math>K</math> și <math>L</math> mijloacele segmentelor <math>AB</math>, <math>BC</math>, <math>CD</math>, respectiv <math>DA</math> și cu <math>M</math>,<math>N</math>,<math>P</math> și <math>Q</math> mijloacele segmentelor <math>EF</math>, <math>FG</math>, | ||
<math>GH</math>, respectiv <math>HE</math>. Arătați că: | <math>GH</math>, respectiv <math>HE</math>. Arătați că: | ||
<li><i> a) punctele <math>I</math>,<math>M</math> și <math>K</math> sunt coliniare dacă și numai dacă <math>AC=BD</math>. | <li><i> a) punctele <math>I</math>,<math>M</math> și <math>K</math> sunt coliniare dacă și numai dacă <math>AC=BD</math>. | ||
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'''Soluție.''' | '''Soluție.''' | ||
a)Fie <math>AE = BF = CG = x</math> și versorii <math>\overrightarrow{i}</math> și <math>\overrightarrow{j}</math> | a)Fie <math>AE = BF = CG = x</math> și versorii <math>\overrightarrow{i}</math> și <math>\overrightarrow{j}</math> ai vectorilor <math>\overrightarrow{A C}</math>, respectiv <math>\overrightarrow{B D}</math>. | ||
Deoarece <math>I</math> și <math>M</math> sunt mijloacele segmentelor <math>AB</math>, respectiv <math>EF</math>,obținem: | Deoarece <math>I</math> și <math>M</math> sunt mijloacele segmentelor <math>AB</math>, respectiv <math>EF</math>, obținem: | ||
<math>\overrightarrow{I M} = \frac{{1}}{2} \cdot (\overrightarrow{A E}+\overrightarrow{B F}) =\frac{{x}}{2} \cdot | <math>\overrightarrow{I M} = \frac{{1}}{2} \cdot (\overrightarrow{A E}+\overrightarrow{B F}) =\frac{{x}}{2} \cdot | ||
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\overrightarrow{i} + \frac{{BD}}{2} \cdot \overrightarrow{j} </math> (2) | \overrightarrow{i} + \frac{{BD}}{2} \cdot \overrightarrow{j} </math> (2) | ||
Din (1) și (2) rezultă ca <math>I</math>,<math>M</math> și<math>K</math> sunt coliniare dacă și numai dacă <math>AC = BD</math>. | Din (1) și (2) rezultă ca <math>I</math>,<math>M</math> și <math>K</math> sunt coliniare dacă și numai dacă <math>AC = BD</math>. | ||
b)Notăm <math>\overrightarrow{i} +\overrightarrow{j} = \overrightarrow{O R}</math> și <math>\overrightarrow{-i} +\overrightarrow{j} = \overrightarrow{O S}</math>. | b) Notăm <math>\overrightarrow{i} +\overrightarrow{j} = \overrightarrow{O R}</math> și <math>\overrightarrow{-i} +\overrightarrow{j} = \overrightarrow{O S}</math>. | ||
Se observă că semidreptele (OR și OS sunt bisectoarele unghiurilor COD,respectiv AOD.Ca în (1),deducem că <math>\overrightarrow{P K} =\overrightarrow{I M} = \frac{{x}}{2} \cdot (\overrightarrow{i}+\overrightarrow{j}) =\frac{{x}}{2} \cdot \overrightarrow{O R}</math>,iar <math>\overrightarrow{J N} =\overrightarrow{Q L} = \frac{{x}}{2} \cdot (\overrightarrow{-i}+\overrightarrow{j}) =\frac{{x}}{2} \cdot \overrightarrow{O S}</math>. | Se observă că semidreptele (OR și OS sunt bisectoarele unghiurilor COD,respectiv AOD.Ca în (1),deducem că <math>\overrightarrow{P K} =\overrightarrow{I M} = \frac{{x}}{2} \cdot (\overrightarrow{i}+\overrightarrow{j}) =\frac{{x}}{2} \cdot \overrightarrow{O R}</math>,iar <math>\overrightarrow{J N} =\overrightarrow{Q L} = \frac{{x}}{2} \cdot (\overrightarrow{-i}+\overrightarrow{j}) =\frac{{x}}{2} \cdot \overrightarrow{O S}</math>. | ||
Fiind bisectoarele a două unghiuri adiacente suplementare,semidreptele (OR și OS sunt perpendiculare ,de unde rezultă că <math>IM \perp JN</math>,<math>JN \perp KP</math> , <math>KP \perp LQ</math> și <math>LQ \perp IM</math>.Dar <math>AC \not= BD</math> , deci <math>I</math>,<math>M</math> și <math>K<math>M</math> sunt necoliniare ,așadar <math>IM \parallel KP</math> , și analog <math>JN \parallel LQ</math>.Notând cu <math>X</math>,<math>Y</math>,<math>Z</math>,<math>W</math> intersecțiile perechilor de drepte <math>IM</math> și <math>JN</math>,<math>JN</math> și <math>KP</math>,<math>KP</math> și <math>LQ</math>,<math>LQ</math> și <math>IM</math> ,din cele de mai înaite rezultă că <math>XYZW</math> este dreptunghi. | Fiind bisectoarele a două unghiuri adiacente suplementare, semidreptele (OR și OS sunt perpendiculare ,de unde rezultă că <math>IM \perp JN</math>,<math>JN \perp KP</math> , <math>KP \perp LQ</math> și <math>LQ \perp IM</math>.Dar <math>AC \not= BD</math> , deci <math>I</math>,<math>M</math> și <math>K<math>M</math> sunt necoliniare ,așadar <math>IM \parallel KP</math> , și analog <math>JN \parallel LQ</math>.Notând cu <math>X</math>,<math>Y</math>,<math>Z</math>,<math>W</math> intersecțiile perechilor de drepte <math>IM</math> și <math>JN</math>,<math>JN</math> și <math>KP</math>,<math>KP</math> și <math>LQ</math>,<math>LQ</math> și <math>IM</math> ,din cele de mai înaite rezultă că <math>XYZW</math> este dreptunghi. | ||
Revision as of 13:15, 4 December 2023
28354 (Florin Bojor)
Fie Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle O} punctul de intersecție a diagonalelor patrulaterului convex Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle ABCD} și punctele , , și Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle H} situate pe segmentele Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle OA} , Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle OB} , Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle OC} , respectiv Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle OD} , astfel încât Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle AE = BF = CG = DH} . Notăm cu Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle I} ,Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle J} ,Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle K} și Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle L} mijloacele segmentelor Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle AB} , Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle BC} , Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle CD} , respectiv Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle DA} și cu Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle M} ,Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle N} ,Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P} și Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle Q} mijloacele segmentelor Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle EF} , Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle FG} , Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle GH} , respectiv Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle HE} . Arătați că:
Soluție.
a)Fie Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle AE = BF = CG = x}
și versorii Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \overrightarrow{i}}
și Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \overrightarrow{j}}
ai vectorilor Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \overrightarrow{A C}}
, respectiv Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \overrightarrow{B D}}
.
Deoarece Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle I} și Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle M} sunt mijloacele segmentelor Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle AB} , respectiv Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle EF} , obținem:
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \overrightarrow{I M} = \frac{{1}}{2} \cdot (\overrightarrow{A E}+\overrightarrow{B F}) =\frac{{x}}{2} \cdot \overrightarrow{i} + \frac{{x}}{2} \cdot \overrightarrow{j} } . (1)
Cum Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle K} este mijloxul segemntului Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle CD} ,deducem:
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \overrightarrow{I K} = \frac{{1}}{2} \cdot (\overrightarrow{A C}+\overrightarrow{B D}) =\frac{{AC}}{2} \cdot \overrightarrow{i} + \frac{{BD}}{2} \cdot \overrightarrow{j} }
(2)
Din (1) și (2) rezultă ca Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle I} ,Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle M} și Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle K} sunt coliniare dacă și numai dacă Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle AC = BD} .
b) Notăm Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \overrightarrow{i} +\overrightarrow{j} = \overrightarrow{O R}} și Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \overrightarrow{-i} +\overrightarrow{j} = \overrightarrow{O S}} .
Se observă că semidreptele (OR și OS sunt bisectoarele unghiurilor COD,respectiv AOD.Ca în (1),deducem că Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \overrightarrow{P K} =\overrightarrow{I M} = \frac{{x}}{2} \cdot (\overrightarrow{i}+\overrightarrow{j}) =\frac{{x}}{2} \cdot \overrightarrow{O R}} ,iar Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \overrightarrow{J N} =\overrightarrow{Q L} = \frac{{x}}{2} \cdot (\overrightarrow{-i}+\overrightarrow{j}) =\frac{{x}}{2} \cdot \overrightarrow{O S}} .
Fiind bisectoarele a două unghiuri adiacente suplementare, semidreptele (OR și OS sunt perpendiculare ,de unde rezultă că Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle IM \perp JN} ,Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle JN \perp KP} , Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle KP \perp LQ} și Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle LQ \perp IM} .Dar Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle AC \not= BD} , deci Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle I} ,Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle M} și Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle K<math>M} sunt necoliniare ,așadar Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle IM \parallel KP} , și analog Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle JN \parallel LQ} .Notând cu Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle X} ,Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle Y} ,Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle Z} ,Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle W} intersecțiile perechilor de drepte Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle IM} și Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle JN} ,Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle JN} și Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle KP} ,Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle KP} și Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle LQ} ,Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle LQ} și Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle IM} ,din cele de mai înaite rezultă că Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle XYZW} este dreptunghi.