已知x-y=1,求x^2减y^2加3x减5y

问题描述:

已知x-y=1,求x^2减y^2加3x减5y

x=y+1
x^2=y^2+2y+1
x^2-y^2+3x-5y
=y^2+2y+1-y^2+3(y+1)-5y
=2y+1+3y+3-5y
=4