High School Math : How to find the equation of a circle

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #1 : How To Find The Equation Of A Circle

The center of a circle is  and its radius is . Which of the following could be the equation of the circle? 

Possible Answers:

Correct answer:

Explanation:

The general equation of a circle is , where the center of the circle is  and the radius is .

Thus, we plug the values given into the above equation to get 

Example Question #2 : How To Find The Equation Of A Circle

Which one of these equations accurately describes a circle with a center of and a radius of ?

Possible Answers:

Correct answer:

Explanation:

The standard formula for a circle is , with the center of the circle and the radius.

Plug in our given information.

This describes what we are looking for.  This equation is not one of the answer choices, however, so subtract from both sides.

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