Question

若代数式-(mx的平方-5x+3)-2(x的平方+nx-2)-x的值与x的取值无关 求(m+n)(m-n)搞快.马上要.

Answer 1

-(mx的平方-5x+3)-2(x的平方+nx-2)-x

=-(mx²-5x+3)-2(x²+nx-2)-x

= -mx²+5x-3 - 2x²- 2nx+4 -x

= -（m+2）x²+(5-2n)x+1

与x的取值无关,

则m+2=0,5-2n=0

m= -2 ,n=5/2

(m+n)(m-n)

=m²-n²

=4-25/4

= -9/4