# Is #100 - 20y + y^2# a perfect square trinomial and how do you factor it?

##### 1 Answer

Yes, your expression is a perfect square trinomial.

#### Explanation:

A **trinomial** is simply a polynomial that has three terms. Your expression is a trinomial because it has three terms:

In order for it to be a *perfect square trinomial*, it has to be equal to the **square of a binomial**, which is a polynomial that has *two terms*.

You can factor your expression in order to check if it meets this criterion. A trinomial can be factored as a *product of two binomials*, so all you have to do is see if these two binomials are **equal**

The right side of this equation is equal to

Now match the terms of your original expression with these terms

You need to have

- If
#b=10# , then

This solution is not valid because the expression would be equal to

- If
#b=-10# , then

This is a valid solution, since

Therefore, your original expression is a *perfect square trinomial* because you can write it as