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Express each of the following as an algebraic sum of sines or cosines :(i) 2sin 6x cos 4x(ii) 2cos 5x din 3x(iii) 2cos 7x cos 3x(iv) 2sin 8x sin 2x |
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Answer» (i) 2sin 6x cos 4x = sin (6x+4x) + sin (6x-4x) = sin 10x + sin 2x Using, 2sinAcosB = sin (A+ B) + sin (A - B) (ii) 2cos 5x sin3x = sin (5x + 3x) – sin (5x – 3x) = sin8x – sin2x Using, 2cosAsinB = sin(A + B) – sin (A - B) (iii) 2cos7xcos3x = cos (7x+3x) + cos (7x – 3x) = cos10x + cos 4x Using, 2cosAcosB = cos (A+ B) + cos (A - B) (iv) 2sin8 x sin2 x = cos (8x - 2x) – cos (8x + 2x) = cos6x – cos10x Using, 2sinAsinB = cos (A - B) – cos (A+ B) |
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