Using relations of sin and cosine to find answer question.
Cos (23pi/2) = cos ( pi/2) = 0 Sin(theta) = 0 at nowhere BETWEEN 0 and pi/2
it DOES equal 0 AT 0 But your question stated theta>0
We know that 23pi/2 is in between 270°(3pi/2) and 360°(2pi).
So, it's reference angle is 24pi/12 - 23pi/2 (because 2pi/1 is equal to 24pi/12).
The reference angle will be pi/12.
We know that sin+cos is equal to 90. and 90° in radians is pi/2. So, (pi/2) - (pi/12) will give you the value of theta, which is 5pi/12