The radii of two concentric circles with center O are 26 cm and 16 cm. Chord AB of the larger circle is tangent to the smaller circle at C and AD is a diameter. What is the length of CD?
Explanation:
In right ∆AOC, AC = OA2-OC2 = 262-162 = 420 = 2105.
⇒ AB = 4√105
Now, since AD is the diameter, hence ∠ABD = 90° [Angle subtended by diameter on circle is always right angle.]
∴ In right ∆ABD AD2 = AB2 + BD2 ⇒ 522 = (4√105)2 + BD2 ⇒ BD2 = 2704 – 1680 = 1024 ⇒ BD = 32.
Now in ∆CBD ⇒ CD2 = CB2 + BD2 ⇒ CD2 = 420 + 1024 = 1444 ⇒ CD = 38
Hence, option (d).
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