Blue circle puZZle

Geometry Level 2

interesting geometry problem interesting geometry problem Hello genius minds, this is Mind Your Concept welcoming you to this math's paradox. I am Swaroop Dora.

Question: A arbitrary blue circle is chosen inside a big circle. The distance of blue circle from big circle in north, south, east and west directions are 1, 5, 2, and 3 respectively. What is the radius of the blue circle?

I found this puzzle interesting because it can be fun if we ask taking the big circle as earth and blue circle as moon. Giving required distances we can ask for radius of moon.

3 1 5 Can't be found 2

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3 solutions

Nibedan Mukherjee
Jan 20, 2020

Let the radius of the blue circle is r r . The power from the center of the blue circle to the big circle is: ( 1 + r ) ( 5 + r ) = ( 2 + r ) ( 3 + r ) r 2 + 6 r + 5 = r 2 + 5 r + 6 r = 1 (1+r)(5+r)=(2+r)(3+r) \\ r^2+6r+5=r^2+5r+6 \\ r=1

Same way - this is the intersecting chords theorem

Chris Lewis - 1 year, 4 months ago

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So in this theorem the intersecting chords doesn't have to be right angle? Thanks for sharing, Chris!

Saya Suka - 1 year, 4 months ago
Saya Suka
Jan 19, 2020

Let r be the radius of blue circle.
(2r + 6) * (2r + 5) = sqrt{[(r + 2)² + (r + 5)²] * [(r + 1)² + (r + 3)²]} + sqrt{[(r + 2)² + (r + 1)²] * [(r + 5)² + (r + 3)²]}.
Doing all the required expansion, in the end it becomes.
0 = 2r³ + 9r² + 4r - 15.
We get
r = -3 or r = -2.5 or r = 1



Are you using Tolemy?

Isaac YIU Math Studio - 1 year, 4 months ago

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it's Ptolemy I reckon?

nibedan mukherjee - 1 year, 4 months ago

I don't usually know the name of theories, just doing it the way I've seen used before.

Saya Suka - 1 year, 4 months ago

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