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Difficulty: 4/102022 NMTC 2022 (QII-51)

ΔABC is inscribed in circle with center O. If AB = 17 cm, BC = 10 cm and AC = 9 cm, then find the length of AO.

Guide / Hint

Hint 1: Find the area of using Heron's formula: where . The area is 36.

Hint 2: Use the circumradius formula to find the circumradius .

Hint 3: Substitute and into the formula and solve.

Solution

Step 1 (Find Semiperimeter): The side lengths of are cm, cm, and cm. We find the semiperimeter :

Step 2 (Calculate Triangle Area using Heron's):

Step 3 (Apply Circumradius Formula): The radius of the circumcircle (which equals the length of , where is the center) is given by:

Step 4 (Conclusion): The length of is exactly 10.625 cm (or 85/8).

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