①化简求值:2(x^2y+xy)-3(x^2y-xy)-4x^2y,其中x=1,y=-1.②已知多项式3x^2+my-8与多项式-_数学解答

①化简求值:2(x^2y+xy)-3(x^2y-xy)-4x^2y,其中x=1,y=-1.
②已知多项式3x^2+my-8与多项式-nx^2+2y+7的差中,不含有x,y求n^m+mn的值.

人气：312 ℃　时间：2019-12-11 09:46:08

解答

2(x^2y+xy)-3(x^2y-xy)-4x^2y
=2x²y+2xy-3x²y+3xy-4x² y
=-5x²y+5xy
=5-5
=0
(3x^2+my-8)-(-nx^2+2y+7)
=3x²+my-8+nx²-2y-7
=(3+n)x²+(m-2)y-15
∵不含有x,y
∴3+n=0
m-2=0
∴m=2
n=-3
∴n^m+mn
=9-6=3