How to calculate distance from the hole in golf?

QUESTION:
When golf is on TV, you see pros walk off steps from a known point, such as a sprinkler head, to their ball. But since their ball, the hole and that known point don’t form a straight line, how do they know the exact distance to the hole?

In my mind, those three points form a triangle, which most likely doesn’t have a right angle, so even Pythagoreus would have difficulty with the math. How do they get it down to a precise number like 171 yards?

ANSWER:

Answer by gladerade
Professional golfers and their caddies spend hours walking off and measuring the course from various points (such as the sprinkler heads, rocks, etc) to the middle of the green in the days preceeding the tournament and hit many shots from those points during practice rounds — which is why if you’ve ever watched an early week PGA practice round, you see golfers hitting multiple balls from one spot on almost every hole. Then, each day of the tournament, the caddies go out and find the hole placement and walk off how far it is from the center of the green.
All of this information is on that little book (pad of paper) that the caddy or golfer carries and occationally TV shows them looking at.