What is cotangent of 270 degrees?

Firstly, with the unit circle (r=1) we need to know that:

at 270 degrees our coordinates are (0, -1)

sine(270 degrees) = -1

cosine(250 degrees) = 0

cotangent = cosine / sine

therefore: cot ( 270 degrees) = 0/-1 = 0

The answer is 0.