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Math Forum » Discussions » Math Topics » geometry.pre-college.independent

Topic: Alternate Formula for Radius of a Circle
Replies: 3   Last Post: Jul 6, 2006 5:41 PM

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Jonas

Posts: 23
Registered: 4/9/06
Alternate Formula for Radius of a Circle
Posted: Jul 6, 2006 2:51 AM
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I am doing some review of basic math. I ran accross an answer in a
Schwaum's book that I can't make sense of and I wasn't able to derive
the formula either. Here is the problem.

Find the standard equation of the circle with center at (1,3) and
tangent to the line
5x-12y-8=0.

To find the radius, the book uses the following formula
|5(1)-12(3)-6|/13=3.

I solved the problem in a different way and got the right answer but I
couldn't figure out how the above equation was created and why it
works.

Any insight you could give would be appreciated.

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