Question

(3x-y)^2-(2x+y)^2-5x(x-y)=?

知道请回答,要快哦

Answer 1

(3x-y)2-(2x+y)2-5x(x-y) 其中x=0.2 y=0.01
解：原式=(3x-y+2x+y)(3x-y-2x-y)-5x2+5xy
=5x(x-2y)-5x2+5xy=5x2-10xy-5x2+5xy=-5xy
把x=0.2 y=0.01代入上式得
原式=-5×0.2×0.01= -0.01

Answer 2

(3x-y)^2-(2x+y)^2-5x(x-y)

=9x^2-6xy+y^2-(4x^2+4xy+y^2)-5x^2+5xy

=9x^2-6xy+y^2-4x^2-4xy-y^2-5x^2+5xy

=(9x^2-4x^2-5x^2)-(6xy+4xy-5xy)+(y^2-y^2)

=-5xy