the answer is (c)sin0
remember the following so you wont get confused
A) trig functions + reciprocal trig functions
[tex]sin x = \frac{1}{csc x}[/tex] [tex]csc x = \frac{1}{sin x}[/tex]
[tex]cos x = \frac{1}{sec x}[/tex] [tex]sec x = \frac{1}{cos x}[/tex]
[tex]tan x = \frac{1}{cot x}[/tex] [tex]cot x = \frac{1}{tan x}[/tex]
B) Quotient Identities
[tex]tan x = \frac{sin x}{cos x}[/tex] [tex]cot x = \frac{cos x}{sin x}[/tex]
C) Pythagorean Identities
[tex]sin^2 x + cos^2 x =1[/tex]
[tex]1 + tan^2 x = sec^x [/tex]
[tex]1 + cot^2 x = csc^2 x [/tex]
there are also half angle identities, etc. but those 3 above should be enough for now