Question

what must be added to 2 x cube minus 4 x + 9 to get 5 x cube minus 13

Answer 1

to get 5x^3-13 from 2x^3-4x+4

5x^3-13-(2x^3-4x+4)

5x^3-13-2x^3+4x-4

3x^3+4x-17