Python Math

Game Engine Game Engine Support and Discussion
#1

Ok, so I’m working on a .blend with triangles, heres and example of what the triangle would look like.
http://i135.photobucket.com/albums/q146/andrew-101/Blender/example.jpg
What I’m doing is trying to get angle A.
a,b,c are known values so according to good old trigonometry:

a^2 = b^2 + c^2 - 2bc*cosA

So, I’m after A and after rearranging the formula I get this:

cosA = (a^2)/(b^2 + c^2 - 2bc)

This wouldn’t be problem on my calculator, but in python how do I find the exact value of A not the value of cosA, I looked at the math module but I couldn’t figure out what to use.

And also, did I rearrange it correctly?

#2

it’s an equation isn’t… so if you divide everything by Cos… will get rid of the get rid of the Cos in front of the A? so CosA/cos = ((a^2)/(b^2 + c^2 -2bc))/cos

so A = ((a^2)/(b^2 + c^2 -2bc))/cos ?? hmm I have no idea if this is correct.

#3

It could work, it makes sense, I’ll give it a try later because I’m a bit short on time atm.

Edit, nvm that wont work. cos is a ratio so it has to be cos45 or something, cos by itself it meaningless really.

#4

this should help…

  • the angles of a triangle if one knows the three sides: http://upload.wikimedia.org/math/b/c/5/bc56ad69fbfa82874c9bddf7d4125330.png
#5

code: A = acos((b2 + c2 - a**2)/(2bc))

:slight_smile:

#6

REiKo Rhiemer;
Thanks, I tried using acos but got wierd results, it was only last night that I realised that it not onlyt takes radian input but it gives a radian output. At least I know its acos now.

#7

I am glad you got it to work. Inverse trigonometric functions are fun :).

#8

Radians become degrees if multiplied by 180, right?

#9

1 rad = 180/pi;
so pi rad = 180 degrees;
pi/2 = 90 degrees and so on;

Conversely 1 degree = pi/180;
so 90 degree = pi/2

#10

rad/degree conversions are easy beans if you just use math.radians(number in degrees) or math.degrees(number in radians)

#11

Hah, I saw that function but didn’t know what it was for.