Answer:
Undefined.
Step-by-step explanation:
Comment
Let's begin by discussing why a calculator throws up and gives an error when Tan(pi/2) is entered.
Start by entering Tan(89) which is 1 degree from pi/2. The calculator is very well behaved when you do that, but look at how big Tan(89) is. 57.29. That's pretty big as these things go.
I was taught that the answer to Tan(pi/2) was infinity which I think is no longer in vogue. I think you should be answering Undefined.