Question

How do you factor `3x^4+15x^2-72`?

Answer 1

`3(x^2 - 3)(x^2 + 8)`

Explanation:

Call x^2 = X, and factor the trinomial in parentheses.
`f(x) = 3(X^2 + 5X - 24).`
Find 2 numbers knowing sum (b = 5) and product (c = -24).
They are: -3 and 8.
`f(x) = 3(X - 3)(X + 8) = 3(x^2 - 3)(x^2 + 8)`