Question

若代数式(mx2-x2+1)-(3x2-2y2+5x)的值与x无关,试求代数式2m2-（m2+9m)-m的值.

Answer 1

(mx2-x2+1)-(3x2-2y2+5)

=mx2-x2+1-3x2+2y2-5

=(m-4)x2+2y2-4

与x无关则x2系数为0

m-4=0

m=4

2m2-（m2+9m)-m

=2m2-m2-9m-m

=m2-10m

=16-40

=-24