1) (x^4+7x^3+7)-(2x^4-4x^3+1)

Question

= -x^4+3x^3+6

2) (3n^3+n^2-n-4)+(5n^3-4n^2+11)

= 8n^3-3n^2-n+11

Answer 1

You're on the right track...

1. expand it and write it out when it is a subtraction:
(x^4+7x^3+7)-(2x^4-4x^3+1)
= x^4+7x^3+7) -2x^4+4x^3-1
= -x^4 + 11 x^3 + 6

2. space out your terms to avoid losing some of them.
(3n^3 + n^2 -n -4)+(5n^3 -4n^2 + 11)
= 3n^3 + n^2 -n -4 + 5n^3 -4n^2 + 11
= 8n^3 - 3n^2 -n + 7

Answer 2

for #1 i did
(x^4+7x^3+7)-(2x^4-4x^3+1)
= x^4+7x^3+7-2x^4-4x^3-1
= -x^4+3x^3+6

so why is it wrong?

Answer 3

because you see that when you expanded the polynomials after the -2x^4 yu have a - instead of a positive because recall that when the brackets expand - and - = +.

That is the only thing you did wrong.

Good luck! you are on the right track though.

Answer 4

ok thank you

Answer 5

no problem:)