Question

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

Answer 1

x=m^2-2mn+n^2

x=(m-n)^2

x=(1-2)^2

x=1

y=m^2-2mn-n^2

y=m^2-2mn+n^2-2n^2

y=(m-n)^2-2n^2

y=1-2*2^2

y=-7

x-[y-2x-（x-y）]

=x-[y-2x-x+y]

=x-[2y-3x]

=x-2y+3x

=4x-2y

=4*1-2*(-7)

=4+14

=18