# Really basic trig question

• December 10th 2011, 02:39 PM
Nervous
Really basic trig question
OK:
arsin(sin(5p\7)) = 2p/7
arctan(tan(5p/5))= -p/5

Why is the second answer negative?
• December 10th 2011, 02:40 PM
Prove It
Re: Really basic trig question
Quote:

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...
• December 10th 2011, 02:45 PM
skeeter
Re: Really basic trig question
Quote:

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
• December 10th 2011, 02:51 PM
Prove It
Re: Really basic trig question
Quote:

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*}...
• December 10th 2011, 03:04 PM
skeeter
Re: Really basic trig question
Quote:

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 ...
Quote:

arsin(sin(5p\7)) = 2p/7
what else could "p" be?