### SAT Prep Class: Finding the Circumference of a Circle

Check out Bas Rutten's Liver Shot on MMA Surge: http://bit.ly/MMASurgeEp1 SAT Prep Question #14 Question: If the area (A) of a circle is 9π, what is the circumference (C)? In order to solve this problem, you'll need to know the formulas to find the circumference of a circle as well as the area. These are:? C=π(diameter), or C=2π(radius) A=π(radius)? Problems like this provide you with information from which you'll have to work backwards. This is a common problem form, so it's important to make sure you know what you're trying to find out and follow it step by step. ? In this case, you don't yet know the radius or the diameter of the circle, but you do know the area. Work backwards from this by using the area formula to solve for the radius of the circle and then plug it into the circumference formula.? Solve the Problem 1. Since you know the area of the circle, plug it into the area formula. This will give you:? 9π=π(radius)? 2. To solve this equation, first divide both sides by?π. This gives you 9=(radius)?.? 3. To find the radius, take the square root of both sides. The square root of 9 is 3, so know you know that radius=3.? 4. Now that you know the radius of the circle, you can use it in the formula to find the circumference. Plug it in to get:? C=?2π(3) 5. Simplify the equation to make it C=6π. This is your answer. Read more by visiting our page at: http://www.mahalo.com/courses/sat-math-prep/practice-questions/circumference-of-a-circle/

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