Matematika

Pertanyaan

cos x - cos (x-120) - cos (x-240) = 2 cos x

1 Jawaban

  • jawab
    cos A + cos B = 2 cos 1/2(A+B) cos 1/2(A-B)


    cos x - cos (x - 120)- cos (x - 240) = 2 cos x
    cos x - [ cos (x - 120) + cos (x -240)]= 2 cos x

    cos x - [ 2 cos 1/2 (x-120 + x- 240) cos 1/2 (x -120 - x + 240)] =
    cos x - [ 2 cos 1/2 (2x-360) cosĀ  1/2 (120)]
    cos x - [ 2 cos (x - 180) cos (60)]
    cos x - [ 2 cos (x-180) (1/2)]
    cos x - [ cos (x -180)]
    cos x - [ -cos x]
    cos x + cos x
    2 cos x

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