已知x=m^2-2mn+n^2,y=m^2-2mn-n^2,当m=1,n=2时,求x-[y-2x-﹙x-y)]的值
问题描述:
已知x=m^2-2mn+n^2,y=m^2-2mn-n^2,当m=1,n=2时,求x-[y-2x-﹙x-y)]的值
答
x=m^2-2mn+n^2x=(m-n)^2x=(1-2)^2x=1y=m^2-2mn-n^2y=m^2-2mn+n^2-2n^2y=(m-n)^2-2n^2y=1-2*2^2y=-7x-[y-2x-(x-y)]=x-[y-2x-x+y]=x-[2y-3x]=x-2y+3x=4x-2y=4*1-2*(-7)=4+14=18