Giúp mik giải bt này vs

Giải thích các bước giải:

a.Xét $\Delta ANB,\Delta APC$ có:
Chung $\hat A$

$\hat N=\hat P(=90^o)$

$\to \Delta ANB\sim\Delta APC(g.g)$
$\to \dfrac{AN}{AP}=\dfrac{AB}{AC}$

$\to AN\cdot AC=AP\cdot AB$

b.Xét $\Delta ANP,\Delta ABC$ có:

chung $\hat A$

$ \dfrac{AN}{AP}=\dfrac{AB}{AC}$

$\to \Delta ANP\sim\Delta ABC(c.g.c)$

c.Gọi $PE\cap CB=D$

Ta có: $PD//AC(\perp BN)$

$\to \dfrac{EP}{AN}=\dfrac{BE}{BN}=\dfrac{DE}{CN}$

$\to \dfrac{EP}{ED}=\dfrac{NA}{NC}$

Vì $NF//AB(\perp CP)$

$\to \dfrac{NA}{NC}=\dfrac{PF}{FC}$

$\to \dfrac{EP}{ED}=\dfrac{FP}{FC}$

$\to EF//DC\to EF//BC$