Question

已知x-y=1,求x2-y2+x-3y的值

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Answer 1

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

Answer 2

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