Circle Equation PSAT

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Today's video is an explanation of number 15 from section 4 of the PSAT from Wednesday November 2nd, 2016. This problem involves remembering the formula for a circle in the xy-plane and slotting in the appropriate given values for the center. Also, checking answer choices before doing any unnecessary work!
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Since x and y are points on the circle, if you subtract h and k from them (the center coordinates) you get two legs of a triangle, and the radius is their hypotenuse. Therefore, the circle equation is a restatement of the Pythagorean Theorem.

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