Question

Someone please help me!

Can you please help me! I am trying to find a phase angle on my TI84.
I know that Fi is equal to 4.25 from answer book.

tan (Fi)= c1/c2 c1= -1 and c2= -1/2
soo tan(Fi) =2
So, to find Fi, I thought you do,
arctan (2) = Fi, where Fi should be 4.25.

But this doesnt happen.

If I do tan(4.25), I get 2.
But if I do arctan(2), I do not get 4.25. What am I doing wrong? Is there a setting I have wrong?
(BTW, I am in radian mode on my TI84)

thanx