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Question

Which of the following number (s) is/are rational?
A)sin15°.                             B)cos15°
C)sin15°cos15°.                D) sin15°cos75°
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Solution

Option (C).

Sin 15 cos 15 can be written as

= 1/2 2 sin 15 cos 15  (2 sin a cos a = sin 2a)

= 1/2 sin (2 * 15)

= 1/2 sin 30

= 1/2 * 1/2

= 1/4.

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