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☖ Forums → Discussion Forum → Whats the formula?
Whats the formula?
2004-01-16, 7:46 AM #1
I'm in my comp class and I need the formula that, if you have a triangle and all 3 points and their coordinates. How to get the 3 angles of the triangle.

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I felt like destroying something beautiful.
"Nulla tenaci invia est via"
2004-01-16, 8:11 AM #2
I got 15min to figure this out and nothing on the web is helping...

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I felt like destroying something beautiful.
"Nulla tenaci invia est via"
2004-01-16, 8:17 AM #3
2D or 3D coordinates?
Detty. Professional Expert.
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2004-01-16, 8:18 AM #4
Alright, i got a distance method that gets the distance between two points, now I can't remember how to get the angle.

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I felt like destroying something beautiful.
"Nulla tenaci invia est via"
2004-01-16, 8:19 AM #5
2D

I have 3(x,y) points.

|\
|_\

like that, but of course points are user inputed.

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I felt like destroying something beautiful.
"Nulla tenaci invia est via"
2004-01-16, 8:25 AM #6
Sides are a,b,c.
Angles are A,B,C (A is opposite a, B opposite b etc)

calculate A using the cosine rule (a^2=b^2+c^2-2bc.cosA) after working out the lengths of a, b and c

then use the sine rule (a/sinA = b/sinB = c/sinC) to work out the other angles.
Detty. Professional Expert.
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2004-01-16, 8:29 AM #7
Or as a simple algorithm:

(assuming a,b,c already calculated)

A = cos^-1((b^2+c^2-a^2)/2bc);

ratio = a/sinA;

B = sin^-1(b/ratio);
C = sin^-1(c/ratio);
Detty. Professional Expert.
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2004-01-16, 9:08 AM #8
/me has flashbacks of high school *shudder*

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2004-01-16, 9:23 AM #9
Pythagorean Theorem
A^2 + B^2 = C^2
[http://forums.massassi.net/html/biggrin.gif]
Okay.. maybe not...

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Ya know? Common sense? Not really that common...
2004-01-16, 10:10 AM #10
Quote:
<font face="Verdana, Arial" size="2">Originally posted by Charlie:
Pythagorean Theorem
A^2 + B^2 = C^2
[http://forums.massassi.net/html/biggrin.gif]
Okay.. maybe not...</font>


Yeah, that only works in right-angled triangles. Use the Cosine Law that Det posted.



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2004-01-16, 11:30 AM #11
Cosine Rule > You.

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