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secondary 3 | A Maths
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help pls i tried but cant seem to understand help asap thankyousomuchh:)
Date Posted: 2 years ago
Views: 407
sin 3x
= sin (2x + x)
= sin 2x cos x + cos 2x sin x
(using the addition formula for sin (A + B))
= (2 sin x cos x) cos x + (1 - 2 sin²x) sin x
(using the double angle formula for sin 2A and the all-sine form of the double angle formula for cos 2A)
= 2 sin x cos²x + sin x - 2 sin³x
= 2 sin x (1 - sin²x) + sin x - 2 sin³x
(using the identity sin²x + cos²x = 1 to express our result in sines only)
= 2 sin x - 2 sin³x + sin x - 2 sin³x
= 3 sin x - 4 sin³x
= sin (2x + x)
= sin 2x cos x + cos 2x sin x
(using the addition formula for sin (A + B))
= (2 sin x cos x) cos x + (1 - 2 sin²x) sin x
(using the double angle formula for sin 2A and the all-sine form of the double angle formula for cos 2A)
= 2 sin x cos²x + sin x - 2 sin³x
= 2 sin x (1 - sin²x) + sin x - 2 sin³x
(using the identity sin²x + cos²x = 1 to express our result in sines only)
= 2 sin x - 2 sin³x + sin x - 2 sin³x
= 3 sin x - 4 sin³x
See 1 Answer
done
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clear
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Hope this helps
Date Posted:
2 years ago
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