Posted by **John** on Sunday, January 17, 2010 at 12:52pm.

Find the exact value of the trigonometric function:

sec(-pi/12)

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

- trig -
**Reiny**, Sunday, January 17, 2010 at 2:05pm
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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