Seeing diagram solves the problem

Geometry Level 5

A convex polygon of twelve sides is inscribed in a circle and has in some order six sides of length 2 \sqrt { 2 } and six of length 24 \sqrt { 24 } . Find the integral part of the radius of the circle.


The answer is 6.

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2 solutions

Deeparaj Bhat
Mar 11, 2016

Let the angles subtended by sides of length 2 \sqrt2 and 24 \sqrt{24} at the centre be α \alpha and β \beta respectively. Then, 6 ( α + β ) = 2 π α + β = π 3 6(\alpha+\beta)=2\pi \Rightarrow\alpha+\beta=\frac{\pi}{3} 2 R sin α 2 = 2 2R\sin{\frac{\alpha}{2}}=\sqrt2 2 R sin β 2 = 24 2R\sin{\frac{\beta}{2}}=\sqrt{24}

Now, bashing gives the result R = 38 R=\sqrt{38} .

What was the intended solution?

Ahmad Saad
Feb 28, 2016

I too have used the same method.

Niranjan Khanderia - 5 years ago

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Niranjan Khanderia - 4 years, 8 months ago

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