\(\widehat{C}+\widehat{HAC}=90^\circ\) mà \(\widehat{B}+\widehat{C}=90^\circ\)
\(→\widehat{HAC}=\widehat{B}\)
Xét \(ΔAHB\) và \(ΔCHA\):
\(\widehat{HAC}=\widehat{B}(cmt)\)
\(\widehat{AHB}=\widehat{CHA}(=90^\circ)\)
\(→ΔAHB\backsim ΔCHA(g-g)\)
\(→\dfrac{AB}{HA}=\dfrac{CA}{CH}\) (1)
\(CI\) là đường phân giác \(\widehat{C}\)
\(→\dfrac{IA}{IH}=\dfrac{CA}{CH}\) (2)
(1)(2) \(→\dfrac{IA}{IH}=\dfrac{AB}{HA}\)
