# Finding coordinates of a point in a circle with angle

1. Aug 2, 2008

### AlicanC

I have a point (x,y), a distance (d) and an angle (a). I need a method to find a point using x,y,d and a. For example:
http://c.imagehost.org/0836/03082008299.png [Broken]
I will apply this on a 3D environment, but I am not going to use the 3rd dimension so it's safe.
This is also about programming, but I am capable of applying methods in the programming language so I asked it here.

Last edited by a moderator: May 3, 2017
2. Aug 3, 2008

### ZharAngel

$$(x_?,y_?) = (x+d\cos\alpha,y+d\sin\alpha)$$

3. Aug 3, 2008

### AlicanC

Thanks for the answer, but I have a problem. I wrote some code to put this in action. The code starts from "0" and adds "20" to the angle until the vaule is greater than to "360". I don't know why but the code produced this:
http://c.imagehost.org/0346/2008-08-03_092702.png [Broken]
As you can see there are some mistakes. All are getting repeated but the ones I marked. Here is the debug output I get:
As you can see some values are too close. I am really bad at trigonometry, so I can't find the problem.

Last edited by a moderator: May 3, 2017
4. Aug 3, 2008

### futurebird

The center is at (-49, -1082) and your first point, with the angle, 0 is at
(51, -1082) then radius, d, is 100.

So, when the angle is 20 the point should be
$$100(\cos(20)) + -49 \approx 45$$
$$100(\sin(20))+ -1082 \approx -1048$$

But you have:

Drawing at (-8.204959, -991.151611) Angle is 20.000000

5. Aug 3, 2008

### AlicanC

Ah, you are right! I was making calculations with radians.

Thank you both so much! I was trying to figure this out for two days! Normally I post my questions to forums related to coding or just ask my friends, but can't get an answer :D

6. Aug 3, 2008

### ZharAngel

Always a problem if you forget. When I get errors like that, the first thing I do is to check the mode on my calculator. Lol.