(1)AD^2=AE^2+DE^2
AB^2=AE^2+BE^2
上述两式相减得:AD^2-AB^2=DE^2-BE^2=(DE-BE)(DE+BE)
因为AB=AC,AE是三角形的高,所以BE=EC
所以AD^2-AB^2=DE^2-BE^2=(DE-BE)(DE+BE)=BD*CD
(2)结论将会变成AB^2-AD^2=BD*CD
证明过程如下:AD^2=AE^2+DE^2
AB^2=AE^2+BE^2
AD^2-AB^2=DE^2-BE^2=(DE-BE)(DE+BE)=-BD*DC
即AB^2-AD^2=BD*CD