(ax+by)²-(bx+ay)²

问题描述:

(ax+by)²-(bx+ay)²

(ax+by)²-(bx+ay)²=a²x²+2abxy+b²y²-b²x²-2abxy-a²y²=(a²-b²)x²-(a²-b²)y²=(a²-b²)(x²-y²)