Which trigonometric functions do not have real zeros and which trigonometric functions are even?
please explain this to me! :]
3 Answers

y = sec x and y = csc x have no zeros
y = sec x and y = cos x are the only even trig functions out of the six. The graphs of even functions are symmetrical over the yaxis

Trig functions (there are 6) that do not have zero values
are the secant and cosecant (respective reciprocals of the
cosine and sine functions).
Even (trig) functions are those that are symmetric about the
yaxis. If f(x) = f(x) you have an even function. [Among the 6
trig functions that would be the secant and cosine.]

which trigonometric functions do not have real zeros ?