# Arctan and getting a value outside the defined set

• Oct 3rd 2006, 07:28 AM
a4swe
Arctan and getting a value outside the defined set
I want to solve:
2arctan(2)+arcsin(4/5).
I am doing this by setting
arctan(tan(2arctan(2)+arcsin(4/5))
and then by using the addition formula for tangens twice I get arctan(0)=0
But here is the thing, my text book want's it to be pi.
I can't see how it can since the arctan can never be anything outside [-pi/2,pi/2] right?
So what do I do wrong, anyone?
• Oct 3rd 2006, 07:59 AM
ThePerfectHacker
Quote:

Originally Posted by a4swe
I want to solve:
2arctan(2)+arcsin(4/5).
I am doing this by setting
arctan(tan(2arctan(2)+arcsin(4/5))
and then by using the addition formula for tangens twice I get arctan(0)=0
But here is the thing, my text book want's it to be pi.
I can't see how it can since the arctan can never be anything outside [-pi/2,pi/2] right?
So what do I do wrong, anyone?

Where is the equation?
• Oct 3rd 2006, 08:37 AM
a4swe
There is no equation afaik.