# Using Identities to solve the expressions

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• Apr 2nd 2009, 11:52 PM
yeunju
Using Identities to solve the expressions
Problem 1:
Find an exact value. Use double or half angle identity

tan (13pi/12)

My thoughts:
I know that 13pi/12 is in quadrant three and tangent is positive.

I was stuck from the beginning. With the 13pi/12, because it wasn't on the unit circle. So i thought maybe if i turn it into degrees, then i didnt know how to really do that. And i tried thinking of ways to split it, but i only knew how to do it with cosine and sine ones.
• Apr 3rd 2009, 04:08 AM
mr fantastic
Quote:

Originally Posted by yeunju
Problem 1:
Find an exact value. Use double or half angle identity

tan (13pi/12)

My thoughts:
I know that 13pi/12 is in quadrant three and tangent is positive.

I was stuck from the beginning. With the 13pi/12, because it wasn't on the unit circle. So i thought maybe if i turn it into degrees, then i didnt know how to really do that. And i tried thinking of ways to split it, but i only knew how to do it with cosine and sine ones.

[snip]

$\tan \frac{13 \pi}{12} = \tan \frac{\pi}{12} = \tan \left( \frac{\pi}{3} - \frac{\pi}{4}\right)$.
• Apr 3rd 2009, 05:12 PM
stapel
If you'd like to use a half- or double-angle formula, you might want to consider the relationship between pi/12 and, say, pi/6... (Wink)