Question

add the following
(-8x^2-2x+4)+(x^2-9x+7)

Answer 1

(-8x^2-2x+4)+(x^2-9x+7)=
-8x^2+x^2 -2.4x+(-9x) +4+7=
-7x^2 -2.4x-9x +11=

-7x^2 -11.4x +11

Answer 2

(-8x^2-2x+4)+(x^2-9x+7)
to add, we just combine the numerical coefficients (or the numbers before the variable) of the same variables (meaning same letters and same exponents).
thus,
(-8x^2 - 2x + 4 ) + ( x^2 - 9x + 7 )
-7x^2 - 11x + 11

hope this helps~ :)