Hi, im doing a Maths quiz, and am only stuck now on a couple more questions where i was told my anwer is wrong....if anyone could show me the light, it would be appreciated.

1) Given:

x^3+1 = ( x+a ) ( x^2+bx+c )

Find the values of a, b and c. Please enter your answer as a list [in brackets], in the form: [a, b, c]

2) Factorise the following polynomial completely over the integers.

3 x^4+18 x^2+15