Alissa Fong

**MA, Stanford University**

Teaching in the San Francisco Bay Area

Alissa is currently a teacher in the San Francisco Bay Area and Brightstorm users love her clear, concise explanations of tough concepts

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Remember that variables can be added/subtracted/multiplied/divided to both sides of the equation just like numbers. You can use the same rules you would with any single variable equation when you are solving literal equations, which have more than one variable. The goal is to "undo" what is being done to the variable that you must solve for. Use inverse operations to eliminate all other variables and numbers on the same side of the equal sign.

You guys probably already know this formula. The formula for the circumference of a circle is c or circumference equals 2 times Pi times the radius. What if we wanted to solve for r? What we need to do is undo what's being done to r and you notice r is being multiplied by two things, it's being multiplied by 2 and also by pi. So in order to get r by itself I'm going to divide by both of those things. If I divide by 2 pi, then I'm done r is equals to the circumference divided by 2 Pi. That's it.

This problem can be kind of intimidating because a lot of you know Pi is a number it's 3.14 blah, blah, blah, but we just approximate it using, oh we don't approximate it, we notate it by using the Greek symbol pi. So it looks kind of intimidating sometimes. Sometimes students are confused if they should use 3.14 in problems like this but you don't have to. You can just keep the letter Pi when you're solving for r and you're getting it all by itself. This will be useful for you in Geometry class. If ever you're given a circumference and asked to find the radius this is the formula you would use. But you don't have to memorize it, you would just know this relationship and then solve for r.