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secondary 3 | A Maths

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help pls i tried but cant seem to understand help asap thankyousomuchh:)

= 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

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