Question 144455
The tangent function is defined as:

Tan(θ)=Sin(θ)/Cos(θ)

Now, what can we not divide by in the system of real numbers? Correct, 0.

So Cos(θ) cannot equal zero. This occurs at 90 degrees and 270 degrees. (The x value is zero on the unit circle.) In radians, {{{pi/2}}} and {{{3pi/2}}}