Trigonometric Identities
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43. Express cos 3 in terms of cos x. ans. cos3x=4cos^3x-3cosx
47. 2 cos 2y sin 2 y ans. sin 4y
51. sin 16x = 2 sin 8 x cos 8x ans. sin 16x=sin (2(8x))= 2 sin 8x cos 8x
55.cos 4x=2cos2x-1 ans. not an identity
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Trigonometric Identities are investigated.
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43. cos(3x)=cos(2x+x)=cos(2x)cosx-sin(2x)sinx
=(2cos^2x-1)cosx-2sin^2xcosx
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