Really basic trig question

**Nervous** · December 10th 2011, 02:39 PM

OK:
arsin(sin(5p\7)) = 2p/7
arctan(tan(5p/5))= -p/5

Why is the second answer negative?

**Prove It** · December 10th 2011, 02:40 PM

Originally Posted by Nervous

OK:
arsin(sin(5p\7)) = 2p/7
arctan(tan(5p/5))= -p/5

Why is the second answer negative?

The angle must be in the second quadrant...

**skeeter** · December 10th 2011, 02:45 PM

Originally Posted by Nervous

OK:
arsin(sin(5p\7)) = 2p/7
arctan(tan(5p/5))= -p/5

Why is the second answer negative?

uhhh ... arctan((tan(5pi/5)) = \arctan(tan(pi)) = \arctan(0) = 0

**Prove It** · December 10th 2011, 02:51 PM

Originally Posted by skeeter

uhhh ... arctan((tan(5pi/5)) = \arctan(tan(pi)) = \arctan(0) = 0

I must have misunderstood the question, I thought that p was representing some unknown, not $\displaystyle \begin{align*} \pi \end{align*}$ ...

**skeeter** · December 10th 2011, 03:04 PM

Originally Posted by Prove It

I must have misunderstood the question, I thought that p was representing some unknown, not $\displaystyle \begin{align*} \pi \end{align*}$ ...

first solution is ...

arsin(sin(5p\7)) = 2p/7

what else could "p" be?

Thread: Really basic trig question