# Calculating triangle angle

Discussion in 'iOS Programming' started by TodVader, Aug 15, 2009.

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Sep 27, 2005
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#1
Hi. I'm not too sure about the technical words since I speak french but I have a rectangle triangle (with a 90degree angle).

I know both sides (x,y) so to get the hypothenuse, I did this:

float hyp = sqrt((difX * difX) + (difY * difY));

Now, to get the angle I want, I did this:

float rocketAngle = acos(difX/hyp); // difX/hyp should give me the cos of my angle.

I don't understand why it doesn't work. I apply a rotation to my missile with the angle of rocketAngle and it stays straight. My rotation code works if I test it with a static number.

This is done with OpenGL btw.

2. ### -aggie- macrumors P6

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Jun 19, 2009
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Where bunnies are welcome.
#2
Not sure how you're using the rocket angle, but it's probably a degrees to radians issue. acos gives the angle in radians.

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Sep 27, 2005
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#3
Nice! Thankyou, that is probably the problem right there. I will go try this.

4. ### PhoneyDeveloper macrumors 68040

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Sep 2, 2008
#4
That's called a right triangle.

The c library math functions work with radians, not degrees.

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Sep 27, 2005
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#5
Thankyou for the clarification. In french its a "Triangle rectangle"

Btw, this worked perfectly, I can now move on to different things.

Thanks for the help!

6. ### -aggie- macrumors P6

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#6
Glad to help. I thought of writing my response en francais, but then no one else would know what I wrote.

Au revoir!