# Math Help - quadratic equation

1. ## quadratic equation

Given that a and b are the roots of the quadratic equation $2x^2+5x-4$ . Hence , find the values of $a^3+b^3$

I know how to find the values of a+b and ab . I am not sure how to expand $a^3+b^3$ . Thanks for any help

2. Originally Posted by mathaddict
Given that a and b are the roots of the quadratic equation $2x^2+5x-4$ . Hence , find the values of $a^3+b^3$

I know how to find the values of a+b and ab . I am not sure how to expand $a^3+b^3$ . Thanks for any help
Note that $a^3 + b^3 = (a + b)^3 - 3a^2b - 3ab^2 = (a + b)^3 - 3ab(a + b)$.