Construction is must

Geometry Level 4

A circle placed against a right angled triangle centred at O is the 14 cm radius.What is the radius of the smaller circle placed in the remaining gap?


The answer is 2.4020.

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1 solution

Akhil Bansal
Nov 23, 2015

Let x x be the radius of smaller circle, Applying pythagoras theorem in triagle O P O OPO' (see figure).
( 14 + x ) 2 = ( 14 x ) 2 + ( 14 x ) 2 \Rightarrow (14+x)^2 = (14-x)^2 + (14-x)^2 14 + x = 2 ( 14 x ) \Rightarrow 14 + x = \sqrt2(14-x) x = 14 ( 2 1 2 + 1 ) = 2.401 x = 14\left(\dfrac{\sqrt2 -1}{\sqrt2 + 1}\right) = 2.401

Moderator note:

Clear setup! The picture helps make it easy to see how you solved the problem.

Same method.

Priyanshu Mishra - 5 years, 6 months ago

Distance from the point of tangency of the circles from the origin.-the
gap-= ( 14 2 14 ) . B u t t h i s i s a l s o d i s t a n c e o f O 1 a n d o r i g i n + x = 2 x + x = 14 ( 2 1 ) . x = 14 2 1 2 + 1 = 2.4020 (14*\sqrt2-14).\\ But~ this~ is~ also~ distance~ of ~O_1~ and ~origin + x~=\sqrt2* x +x =14(\sqrt2-1).~\\ \therefore ~x=14*\dfrac{\sqrt2 - 1}{\sqrt2+1}=2.4020

Niranjan Khanderia - 5 years, 3 months ago

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