# Thread: Help please, 4 hours and I still can't solve this!

1. ## Help please, 4 hours and I still can't solve this!

Hi everyone,

Sorry to bother, I've been searching for 4 hours for a solution to this and it feels like such a long time ago from when I did this in high school/uni, whichever it was, that my head is about to explode.

I don't know angle z nor ?; I know every other variable I've written there including y and w. The purpose of this is to find the angle at which the circle must be shot against the top wall so that it goes exactly to the point where the bottom left angle w is. The collision against the wall is perfecty ellastic so z = z. What am I missing so that I can find the angle z here? I think I need one more piece of information and I can come up with the equation but for the life of me I can't figure it out =( I must be forgetting some law of similar triangles.

Thank you

2. ## Re: Help please, 4 hours and I still can't solve this!

I don't understand something in the diagram. The double hash marks (bottom and top) typically mean that both line segments have the same length. In this case that's impossible because it implies that angle z is both 90 degrees and also less than 90 degrees. So what do the hash marks mean?

-Dan

3. ## Re: Help please, 4 hours and I still can't solve this!

Sorry! I meant the lines are parallel. I forgot how to notate that then.

Anyway, I figured it out using some pool angles: Billiards 101: How to Do a Bank Shot—The Complete Idiot’s Quick Guide (if anyone else ever needs to figure the same thing out).

Phew, finally! after 6 hours, I still don't quite grasp exactly what is going on (that must be the trig concept I was missing), but it works :P

4. ## Re: Help please, 4 hours and I still can't solve this!

Originally Posted by saintseiya
Sorry! I meant the lines are parallel. I forgot how to notate that then.

Anyway, I figured it out using some pool angles: Billiards 101: How to Do a Bank Shot—The Complete Idiot’s Quick Guide (if anyone else ever needs to figure the same thing out).

Phew, finally! after 6 hours, I still don't quite grasp exactly what is going on (that must be the trig concept I was missing), but it works :P
Hmmm...Your notation might be correct. I seem to recall something like that.

I've looked at the problem and I think we need more information.

-Dan