# Perfect Square Trinomials

Like the difference of squares formula, perfect square trinomial formulas are very common on the test.

For example, .

Note: In a perfect square trinomial, the middle term is twice the product of the square roots of the outer terms.

Example

If , then

A.  â€“4
B.  4
C.  8
D.  16
E.  64

by the formula

by cubing both sides of the equation

by the rule