证明:作AD⊥BC,交BC于D
∵AB = AC
∴D是BC的中点
∴BD = DC
根据勾股定理,有
AB²=AD²+ BD² = AD² + BD²
AP²= AD² + PD²
∴ AB²-AP² = BD²-PD²
∵ PB × PC = (BD - PD)(CD + PD) = BD²-PD²
∴AB² - AP² = PB × PC
证明:作AD⊥BC,交BC于D
∵AB = AC
∴D是BC的中点
∴BD = DC
根据勾股定理,有
AB²=AD²+ BD² = AD² + BD²
AP²= AD² + PD²
∴ AB²-AP² = BD²-PD²
∵ PB × PC = (BD - PD)(CD + PD) = BD²-PD²
∴AB² - AP² = PB × PC