Calculate angle of triangle Python

I'm trying to find out the angle of the triangle in the following, I know it should be 90 degrees, however I don't know how to actually calculate it in the following:

enter image description here

Here's what I've tried:

angle = math.cos(7/9.899)
angleToDegrees = math.degrees(angle)

returns: 43.XX

What am I doing wrong?

Solution

It's a little more compicated than that. You need to use the law of cosines

>>> A = 7
>>> B = 7
>>> C = 9.899
>>> from math import acos, degrees
>>> degrees(acos((A * A + B * B - C * C)/(2.0 * A * B)))
89.99594878743945

This is accurate to 4 significant figures. If you provide a more precise value of C, you get a more accurate result.

>>> C=9.899494936611665
>>> degrees(acos((A * A + B * B - C * C)/(2.0 * A * B)))
90.0