trouble interpreting a problem

Quote:

Originally Posted by frankinaround

express each trigonometric function as a corresponding function of an angle in the first quadrant (0<= Theata <= PIE/2) preceded by a + or - sign:
a)sin 9pie/2
b)sin 7pie
c)sin(-7pie/3)
theres i # of problems, but only posting up to c.

I figure like x is an angle, so f(x) is the function. so they want me to express a trig function as a function of an angle... but isnt a trig function already a function of an angle? and what do they mean preceded by a + or - sign, does that mean f(-x) ? yeah I dont get what they want me to do.

They want you to write it using an angle from $0^o$ to $90^o$

For example

$sinx=sin(x+2n{\pi})$

so for the first one

$\displaystyle\ sin\frac{9{\pi}}{2}=sin\left(4{\pi}+\frac{\pi}{2}\ right)$