We are given two concentric circles k1 and k2. Chord t=10cm of the bigger circle is tangent of the smaller circle. Find the area of ring between two circles.
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If the radius of the larger circle be $b$ cm, and that of the smaller one is $a$ cm
Using this and Pythagoras theorem, $b^2=a^2+5^2$
The area of the ring $=\pi(b^2-a^2)$ cm$^2$