已知x+y=1,那么1/2x^2+xy+1/2y^2的值为多少?
要过程,越详细越好
1/2x^2+xy+1/2y^2
=1/2[x^2+2xy+y^2]
=1/2[x+y]^2
=1/2*1^2
=1/2