A function f is even if f (-x) = f (x) for all x-values in its domain. It is odd if f (- x) = - f (x) for all x-values in its domain. Determine whether each function is even, odd, or neither.
a. f (x) = sin x
b. f (x) = cos x
c. f (x) = tan x
d. f (x) = cot x
e. f (x) = sec x
f. f (x) = csc x