已知x-y=9,xy=8,则x2+y2等于( ) A.100 B.97 C.94 D.91
问题描述:
已知x-y=9,xy=8,则x2+y2等于( )
A. 100
B. 97
C. 94
D. 91
答
∵x-y=9,xy=8,
∴x2+y2=(x-y)2+2xy,
=92+2×8,
=81+16,
=97.
故选B.