If you draw a straight shot at the black into the long rail (0 degrees), and draw a 90 degree cut (towards the red), you can approximate where 45 degrees is (bisect the angle).
Look a little bigger than 45 degrees. So, somewhere around 53.72 degrees?
Ding, ding, ding! We have a winner!
I put this to rest setting it up on my snooker table a la Dr. Dave methodology and Cornerman is exactly correct within allowable deviation. (I just rounded it off to keep it simple.)
As always, PT109 is correct as well....this is a natural in-off shot, a losing hazard (scoring shot) in English Billiards, and so a commonly played line for enthusiasts of that game. This natural in-off can be estimated when the line of your cue stick crosses the face of the top cushion (bottom cushion in the picture but properly termed the "top cushion") at about 10 inches from the center of the corner pocket. When a snooker player leaves himself this shot, I can almost guarantee that it is a positional error. In this case, Stephen Hendry was fortunate that the interfering red ball allowed him to play the black confidently. In fact, if you watch the video, he actually played the standard insurance policy shot when faced with this scenario and chose not to use the interfering red ball as his cue ball "brake". Instead, he played a soft draw which forces the cue ball off of its natural in-off line. Playing natural roll surely would have contacted the lone red with a result of anybody's guess. Playing the shot he chose, the white does curve quite a bit after contact with black although it is hard to discern because they chose that exact instant to change camera angles. The soft draw makes the pot more difficult than the natural roll and it nearly bit him in the butt anyway with the cue ball nearly going in-off the pack into the middle pocket. He truly got away with another error there.
Anyway, this is a pretty straightforward shot for a proper snooker player. One of the aspects about snooker that is easier than pool is that when playing colors off spots, the player ALWAYS knows the angle needed to pot the ball. It is a Pavlovian response. Stephen Hendry has played the black off its spot tens of thousands, hundreds of thousands, millions(?....probably not) of times in his career so he knows EXACTLY the ghost ball position to put it in the pocket. Potting the shot shown is actually not that difficult...I could probably make it half the time. When white is on the cushion in the same line, it becomes incredibly difficult and you are very, very likely to scratch even if you make it.
See the attachment to see the calculations.
P.S. - A snooker player would never, ever give consideration to the fact that this is "a 55 degree cut" or anything of the sort. Been playing the game for about 35 years, have faced this basic shot hundreds, if not thousands of times before. It is just a "thin cut to black pocket, play to avoid the in-off"...enough said. Here is another video of similar but in which the player (Alex Higgins) did
not make a positional error in going to that position; he did it on purpose to lay the groundwork for the following red. Then from that red, he played to almost the same angle on black again to play the same angles to get on the yellow from there. Watch it from the 9:00 to the 10:00 mark and you will see what I mean. There is no calculation involved....just a matter of having done it many, many, many times before:
https://youtu.be/Mga4tirIdTM?t=540
