已知xy=-2,x-y=3,求整式(-3xy-7y)+[4x-3(xy+y-2x)]的值.
问题描述:
已知xy=-2,x-y=3,求整式(-3xy-7y)+[4x-3(xy+y-2x)]的值.
答
原式=(-3xy-7y)+[4x-3xy-3y+6x]
=-3xy-7y+4x-3xy-3y+6x
=-6xy+10(x-y),
当xy=-2,x-y=3时,原式=42.