Answer
$$x^{4} - x^{2} - 20$$
Work Step by Step
We will be using the FOIL method to simplify this expression. Multiply each of the terms within the first set of parentheses with each of the terms in the second set of parentheses:
$$x^{4} + 4x^{2} − 5x^{2} - 20$$
Combine like terms:
$$x^{4} - x^{2} - 20$$