Two concentric circles are of radii 15 cm and 6 cm. What…

Two concentric circles are of radii 15 cm and 6 cm. What is the length (in cm) of the chord of the larger circle that is tangent to the smaller circle?

Show answer & explanation

Correct answer: C

Explanation

The correct answer is option 3 i.e. 6 $\sqrt{21}$

Given that

Two concentric circles radii of 15 cm & 6 cm

Chord AB is a tangent of the inner circle at C

Now by Pythagoras' theorem

AC² = OA² - OC² = 15² - 6² = 225 - 36 = 189

AC = 3 $\sqrt{21}$

The length of the chord AB = 2 * AC = 2 * 3 $\sqrt{21}$ = 6 $\sqrt{21}$

SSC CHSL 2021 PYQ — Question 72