Xét \(\Delta ABN\) và \(\Delta ACP\) có
^\(BAN=\) ^\(CAP\) (góc chung)
^\(ANB=\) ^\(APC\) (\(=90^o\) )
\(\Rightarrow\Delta ABN~\Delta ACP\left(g.g\right)\)
\(\Rightarrow\frac{AB}{AC}=\frac{AN}{AP}\Rightarrow AB.AP=AN.AC\)
Vậy ....
B,
Từ \(\frac{AB}{AC}=\frac{AN}{AP}\Rightarrow\frac{AP}{AC}=\frac{AN}{AB}\)
Xét \(\Delta APNv\text{à}\Delta ACB\)
^\(PAN=\) ^\(CAP\) (góc chung)
\(\frac{AP}{AC}=\frac{AN}{AB}\) (CMT)
\(\Rightarrow\Delta APN~\Delta ACB\left(c.g.c\right)\)
\(\Rightarrow\) ^\(APN=\) ^\(ACP\) (2 GÓC TƯƠNG ỨNG)
KL....( nhớ k cho mk nha)