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Points $A$, $B$, and $C$ are on a circle such that $AB = 8$, $BC = 15$, and $AC = 12$. Find the radius of the circle.

 Mar 28, 2024

Best Answer 

 #1
avatar+14 
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According to the Triangle Inequality, ABC is indeed a triangle, since 8 + 12 > 15.

 

Thus, the radius of the circle is the same as the circumradius of ABC, which can be found by:
\(R = \frac {abc} {4S}\)

 

Where S is the area of the triangle.

 

Using Heron's formula, we get:
\(S = \sqrt { \frac {35} {2} \left( \frac {35} {2} - 8 \right) \left( \frac {35} {2} - 15 \right) \left( \frac {35} {2} - 12 \right)}\)

\(S = \sqrt {\frac {35} {2} \left( \frac {19} {2} \right)\left( \frac {5} {2} \right)\left( \frac {11} {2} \right)}\)

\(S = \frac {5} {4} \sqrt {1463}\)

 

Therefore,

\(R = \frac {2520} {5\sqrt{1463}}\)

\(R = \frac {504\sqrt{1463}} {1463}\)

 Mar 28, 2024
 #1
avatar+14 
+1
Best Answer

According to the Triangle Inequality, ABC is indeed a triangle, since 8 + 12 > 15.

 

Thus, the radius of the circle is the same as the circumradius of ABC, which can be found by:
\(R = \frac {abc} {4S}\)

 

Where S is the area of the triangle.

 

Using Heron's formula, we get:
\(S = \sqrt { \frac {35} {2} \left( \frac {35} {2} - 8 \right) \left( \frac {35} {2} - 15 \right) \left( \frac {35} {2} - 12 \right)}\)

\(S = \sqrt {\frac {35} {2} \left( \frac {19} {2} \right)\left( \frac {5} {2} \right)\left( \frac {11} {2} \right)}\)

\(S = \frac {5} {4} \sqrt {1463}\)

 

Therefore,

\(R = \frac {2520} {5\sqrt{1463}}\)

\(R = \frac {504\sqrt{1463}} {1463}\)

WillBill Mar 28, 2024

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