Question

How do you tell whether the value of cos [(pi)/4] is positive, negative, zero or undefined?

Answer 1

See explanation.

Explanation:

Out of `6` trigonometric function `sinx` and `cosx` are the only two defined for all real values of `x`.

To find if the value is positive, negative or zero you have to know in which quadrant the angle lies. `pi/4 in (0;pi/2)`, so it lies in the first quadrant. For this quadrant all trigonometric functions are positive.