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Ex 3.3, 25 - Prove cos 6x = 32 cos6 x - 48 cos4 x + 18 cos2x - Ex 3.3

Ex 3.3, 25 - Chapter 3 Class 11 Trigonometric Functions - Part 2

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Ex 3.3, 25 Prove that: cos 6 = 32 cos6 48 cos4 + 18 cos2 1 Taking L.H.S. cos 6x = 2(cos 3x)2 1 = 2 ( 4 cos3 x 3 cos x)2 1 Using (a b)2 = a2 + b2 2ab = 2 [(4 cos3 x)2 + (3 cos x )2 2 (4 cos3 x) (3 cos x)] 1 = 2 [(16 cos6x + 9 cos2 x 24 cos4x)] 1 = 2 16 cos6x + 2 9 cos2 x 2 24 cos4x 1 = 32 cos6x 48 cos4x + 18 cos2x 1 = R.H.S. Hence L.H.S. = R.H.S Hence proved

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Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.