(x2-y2)-4(2x2-3y)
问题描述：
(x2-y2)-4(2x2-3y)
答
(x²-y²)-4(2x²-3y)=x²-y²-8x²+12y=-7x²-y²+12y
答
=x²-y²-8x²+12y
=-7x²-y²+12y