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CBSE Class 10 Answered

3sin72/7cos18-4(cos square70 +cos square 20)/7(tan5 tan45 tan 85)
Asked by vinitha123 | 18 Feb, 2010, 11:12: AM
answered-by-expert Expert Answer

(3sin72)/(7cos18)-4(cos270 +cos220)/[7(tan5 tan45 tan 85)] =

We can write,

sin 72 = sin 90-18 = cos 18

Similarly, cos 70 = cos 90-20 = sin 20.

and tan 45 =1

and tan 5 = tan 90-85 = sin 90-85 / cos 90-85 = cos 85 / sin 85 = cot 85

Using these identities,

(3cos18)/(7cos18)-4(sin220 +cos220)/[7((cot85) (1) (tan 85))] =

3/7 - 4/7 = -1/7

Regards,

Team,

TopperLearning.

Answered by | 18 Feb, 2010, 11:26: AM

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