已知x+y=0,xy=-6,则x3y+xy3的值是( ) A.72 B.-72 C.0 D.6
问题描述:
已知x+y=0,xy=-6,则x3y+xy3的值是( )
A. 72
B. -72
C. 0
D. 6
答
∵x+y=0,xy=-6,
∴x3y+xy3=xy(x2+y2),
=xy[(x2+y2+2xy)-2xy],
=xy[(x+y)2-2xy],
=-6×(0+12),
=-72,
故选B.