# How do you solve #-4r^2+21r=r+13# by completing the square?

##### 3 Answers

#### Explanation:

Hence

#### Explanation:

#### Explanation:

Let's start by subtracting

Now we can use the quadratic formula

We have:

Note: The quadratic formula is a formula that is very important and I recommend you to memorize it. At least understand how and when to use it.

Replace the numbers