Perfect square trinomials

Use this to factor an expression into the square of a sum, $(a + b)^2$. It applies when the outer terms are squares of $a$ and $b$, and the middle term is twice their product ($2ab$).

Use this to factor an expression into the square of a difference, $(a - b)^2$. It applies when the outer terms are $a^2$ and $b^2$, and the middle term is negative ($-2ab$).

When factoring a three-term quadratic, first check whether the two outer terms are perfect squares, then verify whether the middle term is twice their product.