ShmoopTube

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Here's your shmoop du jour...

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What is the equation for the circle shown?

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And here are your potential answers...

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If we don't know the formula for a circle, we're basically sunk.

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That formula - just to refresh your brain -- is:

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(x -- h)2 + (y -- k)2 = r2 where (h, k)

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is the center of the circle and r is the radius.

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We just have to figure out the h, k and r. One thing in our court that should make it

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easier is that the circle's middle is the origin, or point 0, 0.

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We can just plug those in for starters, which gives us the equation:

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Quantity x minus 0 squared plus quantity y minus 0 squared equals r squared.

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Get rid of the 0's and we have x squared plus y squared equals.....

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Well, we know r already because the problem gives us 4 and negative 4 here and here...

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so this distance is the radius

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The circle's equation has to equal r squared... which is 16.

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So the answer is D.

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