a, góc ABC + BCA = BAC = 90 ⇒ BCA = 90 - ABC
GÓC ABC + GÓC BAH = GÓC BAC =90⇒BAH = 90 - ABC
⇒ GÓC BCA = GÓC BAH
XÉT TAM GIÁC HBA VÀ TAM GIÁC HAC CÓ
GÓC BHA = GÓC BAC = 90
GÓC BCA = GÓC BAH
⇒ TAM GIÁC HBA ∼ TAM GIÁC HAC
b, TAM GIÁC HBA ∼ TAM GIÁC HAC⇒ \(\dfrac{AB}{AC}=\dfrac{BH}{AB}\)⇒AB x AB = AC x BH
c,ab = 3cm
AC = 4CM
⇒\(\dfrac{AB}{AC}=\dfrac{BH}{AB}=\dfrac{3}{4}\)⇒\(\dfrac{s_{HBA}}{s_{HAC}}=\left\{\dfrac{3}{4}\right\}^2\Rightarrow\dfrac{s_{HBA}}{32}=\dfrac{9}{16}\Rightarrow S_{HBA}=18CM^2\)