Art of Problem Solving
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Power of a Point Theorem/Introductory Problem 1

Problem

Find the value of $x$ in the following diagram:

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Solution

Applying the Power of a Point Theorem, we get $3\cdot(3+5) = x (x+10) \rightarrow x^2 + 10x - 24 = 0$. This factors as $(x+12)(x-2) = 0$. We discard the negative solution since distance must be positive. Thus $x=\fbox{2}$.

Back to the Power of a Point Theorem.