Explanation for an answer got by a calculator. (not an error, an actual answer)

Here is a graph of y=tan(theta)

It illustrates what Geno is telling you  :)

https://www.desmos.com/calculator/jsz7qq1cam

ALSO

It is important to remember that   $$tan\theta=\frac{sin\theta}{cos\theta}$$

and  Cos 270 = 0   Anything divided by 0 is undefined        

The value of tan(-270°) is undefined.

If you approach this by finding these values:

tan(-269°) = -57.2899...

tan(-269.9°) = -572.957...

tan(-269.99°) = -5729.577...

tan(-269.999°) = -57295.779...

The values have a limit of -∞.

If you approach this by finding these values:

tan(-271°) = 57.2899...

tan(-270.1°) = 572.957...

tan(-270.01°) = 5729.577...

tan(-70.001°) = 57295.779...

The values have a limit of ∞.

So, tan(-270°) doesn't equal either -∞ or ∞.