Question

已知x-y=1,求x的平方减y的平方加3x减5y的值

Answer 1

x-y=1

x=y+1

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

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

=y^2+2y+1-y^2+3y+3-5y

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

=4