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In the given figure, O is the center of the circle with radius 20 cm and OD is perpendicular to AB.

If AB = 32 cm, find the length of CD.

In the given figure, O is the center of the circle with radius 20 cm and OD is perpendicular to AB. Circle, Concise Mathematics Solutions ICSE Class 9.

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Answer

Join OA.

In the given figure, O is the center of the circle with radius 20 cm and OD is perpendicular to AB. Circle, Concise Mathematics Solutions ICSE Class 9.

We know that,

Perpendicular from centre to the chord, bisects the chord.

∴ AC = AB2=322\dfrac{AB}{2} = \dfrac{32}{2} = 16 cm.

In right-angled triangle OAC,

By pythagoras theorem,

⇒ Hypotenuse2 = Perpendicular2 + Base2

⇒ OA2 = OC2 + AC2

⇒ 202 = OC2 + 162

⇒ 400 = OC2 + 256

⇒ OC2 = 400 - 256

⇒ OC2 = 144

⇒ OC = 144\sqrt{144} = 12 cm.

From figure,

CD = OD - OC = 20 - 12 = 8 cm.

Hence, CD = 8 cm.

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