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Question

sec 70o sin 20o + cos 20o cosec 70o = ?

(a) 0 (b) 1 (c) -1 (d) 2

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Solution

sec 70o sin 20o+cos 20o cosec 70o

=sin 20ocos 70o+cos 20osin 70o

=sin (90o70o)cos 70o+cos (90o70o)sin 70o

=cos 70ocos 70o+sin 70osin 70o = 1+1 = 2

Hence, the correct choice is (d).


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