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Cos (x + 30°) = ...


 JAWABAN: C

PEMBAHASAN: 

cos (A + B) = cos A cos B – sin A sin B

cos (x + 30°) = cos x cos 30° - sin x sin 30°

cos (x + 30°) = cos x . √3/2 – sin x . ½

cos (x + 30°) = ½ (√3 cos x – sin x)

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