In the equation below, the angle measures are in radians and a is a constant.
Which of the following could be the value of a ?
Useful fact to remember: if and are complementary (i.e., they add up to 90° or radians), then .
So I bet the question is getting at what a must be to make the angles add up to ?
Of course, this question asks “which of the following” and there are actually an infinite number of answers, but that’s one of them.