Last updated at Dec. 8, 2016 by Teachoo

Transcript

Ex 3.3, 15 Prove that cot 4x (sin 5x + sin 3x) = cot x (sin 5x β sin 3x) Solving L.H.S. cot 4x ( sin 5x + sin 3x ) Using sin x + sin y = 2 sin (π₯ + π¦)/2 cos (π₯ β π¦)/2 Putting x = 5x & y = 3x = cot 4x Γ [ 2 sin ((5π₯ + 3π₯)/2) cos ((5π₯ β 3π₯)/2) ] = cot 4x Γ [ 2sin (8π₯/2) cos (2π₯/2)] = 2 cot 4x sin 4x cos x = 2 πππ β‘4π₯/π ππβ‘4π₯ Γ sin 4x Γ cos x = 2 cos 4x cos x Solving R.H.S. cot x ( sin 5x β sin 3x ) Using sin x β sin y = 2 cos (π₯ + π¦)/2 sin (π₯ β π¦)/2 Putting x = 5x & y = 3x = cot x ( 2 cos (5π₯ + 3π₯)/2 sin (5π₯ β 3π₯)/2 ) = cot x ( 2 cos (8π₯/2) sin (2π₯/2)] = cot x ( 2 cos 4x sin x) = 2 cos 4x sin x cot x = 2 cos 4x sin x Γ πππ β‘π₯/sinβ‘π₯ = 2 cos 4x cos x = L.H.S Hence L.H.S. = R.H.S. Hence Proved

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Chapter 3 Class 11 Trigonometric Functions

Serial order wise

About the Author

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.