若(x+y-3)2+(x-y+5)2=0.则x2-y2的值是( ) A.8 B.-8 C.15 D.-15
问题描述:
若(x+y-3)2+(x-y+5)2=0.则x2-y2的值是( )
A. 8
B. -8
C. 15
D. -15
答
∵(x+y-3)2+(x-y+5)2=0,
∴
,
x+y−3=0 x−y+5=0
解得
,
x=−1 y=4
∴x2-y2=1-16=-15.
故选D.