Question

Perform the indicated operation. (7x4 + 11x3 – x2 – 8x + 6) – (-12x4 + 9x2 – 15)

Answer 1

just add the coefficients on the common values such as x^4 or x^3

so
(7x4 + 11x3 – x2 – 8x + 6) – (-12x4 + 9x2 – 15)

(7x^4 + 11x^3 – x^2 – 8x + 6 +12x^4 - 9x^2 +15)

(7+12)x^4+(11)x^3+(-1-9)x^2....) // try to fill in the rest.