在△ABC中,D点是 ∠C的平分线与底边AB的交点,证明下列等式：CD²＝AC·BC－AD·BD.可以用正弦定理证明：设x = 1/2 ∠C y =∠ ADC△ADC中CD/sinA = AD/sinx = AC/siny = uCD = u sinA = u sin(x+y)AD = u sinxAC ...