Question

a=3x2-4xy+2y2,b=x2+2xy-5y2求:1、a+b2、a-b3、若2a-b+c=0

A=3x^2-4xy+2y^2,B=x^2+2xy-5y^2且2A-B+C=0,当x=-2,y=-1时,求C的值

Answer 1

∵2A-B+C=0
∴C=B-2A
=(x²+2xy-5y²)-2(3x²-4xy+2y²)
=x²+2xy-5y²-6x²+8xy-4y²
=-5x²+10xy-10y²
=-5×(-2)²+10×(-2)×(-1)-10×(-1)²
=-20+20-10
=-10