c)Ta có: [tex]\widehat{POE}+\widehat{EOF}=\widehat{POF}=180^o-\widehat{QOF}=180^o-(\widehat{QOB}+\widehat{BOF})=180^o-(\widehat{POA}+\widehat{MOF}) \Rightarrow \widehat{POA}+\widehat{AOE}+\widehat{EOM}+\widehat{MOF} \Rightarrow 2\widehat{POA}+2\widehat{AOE}+2\widehat{MOF}=180^o \Rightarrow 2\widehat{POE}+2\widehat{MOF}=180^o \Rightarrow \widehat{POE}+\widehat{MOF}=90^o \Rightarrow \widehat{POE}=90^o-\widehat{MOF}=90^o-\widehat{BOF}=\widehat{OFQ}[/tex]
d) Từ câu d) ta chứng minh được [tex]\Delta EOP \sim \Delta OFQ\Rightarrow \frac{PE}{OP}=\frac{OQ}{QF}[/tex]
[tex]\Rightarrow PE.QF=OP.OQ=\frac{PQ^2}{4}\Rightarrow PE+QF\geq 2\sqrt{PE.QF}=PQ[/tex]
[TẶNG BẠN] TRỌN BỘ Bí kíp học tốt 08 môn
