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# Geometry Question

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In the circle with center \$Q\$, radii \$AQ\$ and \$BQ\$ form a right angle. The two smaller regions are tangent semicircles, as shown. The radius of the circle with center \$Q\$ is 14 inches. What is the radius of the smaller semicircle? Express your answer as a common fraction. Jun 30, 2018

### 1+0 Answers

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Let   M  be the midpoint of   AQ  and N be the midpoint of BQ

Thus....M and N will be the centers of  both of the smaller semi circles

Connect  M and N

By Euclid, a segment connecting the centers of two tangent circles or semi-circles will pass through the point of tangency

So  MQ   will be the radius  of the semicircle with the diameter AQ  = 14

So MQ  = 7

And call the radius of the smallest semi-circle, r

So....MQN  will form  right triangle with  leg  MQ  = 7, leg  QN  = 14 - r  and

hypotenuse MN = ( 7 + r )

So we have that, by the Pythagorean Theorem

7^2  +  (14 - r)^2 = (7 + r)^2

49 + r^2 - 28r + 196  = r^2 + 14r + 49

196 = 42r

196/42  = r

14/3   = r = the radius of the smaller semi-circle   Jun 30, 2018