(40-x)(20+2x)转换到-2(X-15)的平方=1250?)
问题描述：
(40-x)(20+2x)转换到-2(X-15)的平方=1250?)
答
(40-x)(20+2x)
=-2x^2+80x-20x+800
=-2x^2+60x+800
=-2(x^2-30x-400)
=-2(x^2-30x+225-425)
=-2[(x-15)^2-425]
=-2(x-15)^2+850