分解因式：（x-a)^2-(x-b)^2=?;x+2x^2+x^3=?;5x^3-10x^2+5x=?已知x+y=1,求1/2x^2+xy+1/2y^2的值全要过程

(x-a)^2-(x-b)^2=(x-a+x-b)^2(x-a-x+b)^2=(2x-a-b)^2(-a+b)^2x+2x^2+x^3=x(1+2x+x^2)=x(x+1)^25x^3-10x^2+5x=5x(x^2-2x+1)=5x(x-1)^21/2x^2+xy+1/2y^2=1/2(x^2+2xy+y^2)=1/2(x+y)^2=1/2(1)^2=1/2