Two concentric circles are of diameters 30cm and 18cm. Find the length of the chord of the larger circle which touches the smaller circle.

Explanation

Let the two concentric circles are at center O. Let PQ be the chord of a larger circle which touches the smaller circle at point A.

Therefore, PQ becomes the tangent to the smaller circle

`OA_|_PQ` ( tangent to the circle is perpendicular to the radius through the point of contact )

Diameter of larger circle is 30 given
`
`:. radius = OP =15`

Diameter of smaller circle is 18 given

`:. radius = AP =9`

Applying Pythagoras theorem in `/_\OAP`

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