Answer:
D: Undefined
Explanation:
You can use the unit circle or your calc for this (don't forget to put it in radians!). I will use the unit circle to explain.
Tangent on the unit circle is on the xy lines themselves. tan (π/2) would be on the positive y axis. Remember that tan∅ is sin∅/cos∅ and that the unit circle's radius is always one. If that is the case, the coordinate for tan (π/2) would be (0, 1). If cos is always x and sin is always y, you plug it in for tan∅. The fraction 1/0 is undefined, since you can't divide anything by 0. Therefore, tan (π/2) is undefined.