trig

Find the exact value of the trigonometric function:
sec(-pi/12)

I am not sure how to answer this off the unit circle.

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  1. You should know that
    sec (-pi/12)
    = 1/cos(-pi/12)
    = 1/cos(pi/12)

    You might find it "easier" to visualize degrees than radians, if so, the
    pi/12 radians = 15º

    so we need cos 15º

    cos15 = cos(45-30) ... (I am dropping the º symbol for easier typing)

    = cos45cos30 + sin45sin30
    = (√2/2)(√3/2) + (√2/2)(1/2)
    = (√6 + √2)/4

    and
    cos(-pi/12) = 4/(√6 + √2)

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