已知y-x=2,x-3y=1,则x2-4xy+3y2的值为( ) A.-1 B.-2 C.-3 D.-4
问题描述:
已知y-x=2,x-3y=1,则x2-4xy+3y2的值为( )
A. -1
B. -2
C. -3
D. -4
答
x2-4xy+3y2=(x-3y)(x-y),
∵y-x=2,x-3y=1,
∴x2-4xy+3y2=1×(-2)=-2.
故选:B.