hi there, my book didn't have an example like this so I am not sure what to do to solve it. Please explain how to do it, thanks.
Express the following as linear combinations of p1 = 2 + x + 4x^2, p2 = 1 - x + 3x^2, and p3 = 3 + 2x + 5x^2
a.) -9 - 7x - 15x^2