先化简,再求值:(x+y)(x-y)+(x-y)^2-(x^2-3xy),其中x=2,y=0.5

问题描述:

先化简,再求值:(x+y)(x-y)+(x-y)^2-(x^2-3xy),其中x=2,y=0.5

=x^2-y^2+x^2-2xy+y^2-x^2+3xy =x^2+xy =5