trig

Evaluate giving exact values and identities. Calculator based solutions are not acceptable. Thanks for any help
cos (-5pi/12)

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  1. 5pi/12 radians = 75º

    so cos(-5pi/12) = cos(-75º = cos 75º
    = cos(45+30)º
    = cos45cos30 - sin45sin30
    = √2/2*√3/2 - √/2*1/2
    = (√6 - √2)/4

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