计算 3(2x-7y)(7y+2x)+(4x+5y)(-5y-4x)_数学解答

计算 3(2x-7y)(7y+2x)+(4x+5y)(-5y-4x)

人气：493 ℃　时间：2019-12-17 05:17:00

解答

3(2x-7y)(2x+7y)+(4x+5y)(-5y-4x)
=3((2x)^2-(7y)^2)-(4x+5y)^2
=3(4x^2-49y^2)-(16x^2+25y^2+40xy)
=-4x^2-172y^2-40xy