已知x和y满足2x+3y=5,则当x=4时,代数式3x2+12xy+y2的值是( ) A.4 B.3 C.2 D.1
问题描述:
已知x和y满足2x+3y=5,则当x=4时,代数式3x2+12xy+y2的值是( )
A. 4
B. 3
C. 2
D. 1
答
把x=4代入2x+3y=5得:y=-1,
把x=4,y=1代入3x2+12xy+y2得:
3×16+12×4×(-1)+1=1,
故选D.