Matematika

Pertanyaan

cos 40° +cos 80°+ cos 160° =

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  • cos 80 + cos 40 + cos 160
    =(2.cos (80+40)/2. cos (80-40)/2 ) + cos 160
    = 2cos 60. cos 20 + cos 160
    =2.1/2 .cos 20 + cos 160
    = cos 160+ cos 20
    = 2. cos (160+20)/2 .cos (160-20)/2
    = 2 .cos 90. cos 70
    =2. 0.cos 70
    =0

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