Question : working out cotan of -pi/2 on your calculator

Hi

This is probably a daft question but how do you work out cotan -pi/2 on a calculator? My calculator doesn't have cot/csc/sec buttons (i don't know if any do - perhaps they don't) so i just work these functions out by doing the inverse of tan/sin/cos. Naturally tan isn't defined for pi/2 or -pi/2 as cos is 0 there but cotan is defined there as cotan is cos/sin = 0/1 = 0.

I can see that you can work it out in your head as I have just done but I'm teaching myself these things and wondered if I was missing something obvious.

thanks

Answer : working out cotan of -pi/2 on your calculator

Sorry, I meant
cos( -pi/2)/sin( -pi/2)