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pre-calc help !!!!!!!

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if someone could show me how to solve this problem

1) cos(345°)

  • pre-calc help !!!!!!! - ,

    did you notice that 345 = 360-15 ?
    cos(345)
    = cos15

    cos15 = cos(45-30)
    = cos45cos30 + sin45sin30
    = (√2/2)(√3/2) + (√2/2)(1/2)
    = ( √6 + √2)/4

    cos 345 = (√6+√2)/4

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