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O is the circumcentre of the isosceles ∆ABC. Given that AB = AC = 17 cm. and BC = 6 cm. The radius of the circle is
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- 3.015 cm.
- 3.205 cm.
- 3.025 cm.
- 3.125 cm.
- 3.015 cm.
Correct Option: D
According to question , we draw a figure of isosceles triangle ABC in which O is the circumcentre 
AB = AC = 5 cm. (We have assumed to reach answer)
AD ⊥ BC
BD = DC = 3 cm.
In ∆ ADB ,
AD = √AB² - BD²
AD = √5² - 3²
AD = √25 - 9 = √16 = 4 cm.
Let, OA = OC = r cm.
OD = (4 – r) cm.
In ∆ OCD,
OC² = OD² + DC²
⇒ r² = (4 – r)² + 3²
⇒ r² = 16 + r² – 8r + 9
⇒ 8r = 25
⇒ r = 25 ÷ 8 = 3.125
