Perpendicular sector problem

Geometry Level 4

In a circle, two perpendicular sector intersects the yellow circle at 4 point. Then red=6cm and blue=8cm lines drawn. Find the radius of the circle?

None of these 2.5 5 10

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3 solutions

Nibedan Mukherjee
Apr 25, 2020

Let the center of the circle be O O , the end points of the line segment of length 8 8 cm. be A A and C C , those of 6 6 cm. line segment be D D and E E and the right angle be at B B . Let the radius of the circle be R R and O A C = O C A = α \angle {OAC}=\angle {OCA}=α . Then D O E = 2 α \angle {DOE}=2α . So, 2 R sin α = 6 , 2 R cos α = 8 R = 3 2 + 4 2 = 25 = 5 2R\sin α=6, 2R\cos α=8\implies R=\sqrt {3^2+4^2}=\sqrt {25}=\boxed 5 cm.

good solution sir!

nibedan mukherjee - 1 year, 1 month ago

Can you please show through a diagram relation between angles OAC and DOE ? Thanks.

Niranjan Khanderia - 1 year, 1 month ago
Swaroop Dora
Apr 23, 2020

nice approach!

nibedan mukherjee - 1 year, 1 month ago

I think you assume red and blue triangles are similar ! They can not be. Angles by chords 6 and 8 can not be equal.
Please correct me if I am wrong.

Your equation 48 3 + 28 = y 2 a c c o r d i n g t o m e i t i s 12 n o t 28. A c c i d e n t a l l y i t s e e m s t w o m i s t a k e s c a n c e l t o g i v e c o r r e c t a n s w e r ! ! ! \dfrac{48}3 +{\color{#3D99F6}{28}}=y^2\\ according~ to~ me~it~ is~ 12~not~28.\\ Accidentally ~it ~seems~two~mistakes~cancel ~to~give~correct~ answer~~ !!!

Niranjan Khanderia - 1 year, 1 month ago

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@Niranjan Khanderia Sir, waiting for your solution. ;) what's your opinion about my approach.

nibedan mukherjee - 1 year, 1 month ago

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Yours is the best and the only correct approach.
My approach was to assume 8 and 6 to be ||. That gives the answer but is not the correct solution since it assumes what is not given. It could be a special case. I am trying to find a correct solution other than your solution.

Niranjan Khanderia - 1 year, 1 month ago

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@Niranjan Khanderia Approbation! That means a lot sir! And I'm sure you will find a better approach than mine. cheers!

nibedan mukherjee - 1 year, 1 month ago

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@Nibedan Mukherjee Thank you.

Niranjan Khanderia - 1 year, 1 month ago

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