化简：(3c-y)^2－(2c+y)^2－5c(c-y)

题目

化简：(3c-y)^2－(2c+y)^2－5c(c-y)
标题和这一条化简（解释）：[(2C-2分之3×y-(C-y)]^2－2分之3×Cy

答案

(3c-y)^2－(2c+y)^2－5c(c-y)=(9c^2-6cy+y^2)-(4c^2+4cy+y^2)-5c^2+5cy
=9c^2-6cy+y^2-4c^2-4cy-y^2-5c^2+5cy
=-5cy
[(2C-2分之3×y-(C-y)]^2－2分之3×Cy = (2c-3/2y-c+y)^2-3/2cy
=(c-1/2y)^2-3/2cy
=c^2-cy+1/4y^2-3/2cy
=c^2-5/2cy+1/4y^2