# Thread: Using Identities to solve the expressions

1. ## 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.

2. 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]
$\tan \frac{13 \pi}{12} = \tan \frac{\pi}{12} = \tan \left( \frac{\pi}{3} - \frac{\pi}{4}\right)$.

3. 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...