已知-x+2y=5,则5(x-2y)^2 -3(x-2y)-60的值为（A）.
A.80 B.10 C.210 D.40
-x+2y=5 -(x-2y)=5 x-2y=-5
5(x-2y)^2 -3(x-2y)-60=5*25-3*5-60=125+15-60=80
若x^m×y^(n-1)是4次单项式,则m,n满足的条件是__m+n=5__.
m+n-1=4 m+n=5
若式子（2×x^2 +ax-y+b）-(2b×x^2-3x+5y-1)的值不含x^2及x项,则a=_-3__,b=___1_.
2x^2 +ax-y+b-2bx^2+3x-5y+1
(2-2b)x^2+(a+3)x-6y+1+b
由题意：(2-2b)=0 b=1
a+3=0 a=-3