Question

What should be substracted from 1 + x -x2 to get 2x + x2

Answer 1

1-x-2x^2

Step-by-step explanation:

Let the unknown number be a.

Given that: 1+x-x^2-a=2x+x^2

1+x-x^2=2x+x^2+a

1+x-x^2-x^2=2x+a

1+x-2x^2=2x+a

1+x-2x^2-2x=a

1+x-2x-2x^2=a

1-x-2x^2=a

Verification

1+x-x^2-(1-x-2x^2)

1+x-x^2-1+x+2x^2

2x+x^2