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New Member
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Nov 11, 2006, 11:29 AM
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Triginometry
I how do I find the angles, if I only know the lengths of the 3 sides?
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Full Member
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Nov 11, 2006, 12:52 PM
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Thank you for posting your question to the Ask Me Help Desk.
If you are given the lengths of 3 sides of a right triangle...
SinΘ = opp/hyp
This means that if you divide the two lengths that correspond to the side opposite the angle you are looking for and the hypotenuse the answer will be sinΘ. You can then take the inverse sin to solve for Θ.
You can also use
cosΘ = adj/hyp which is the adjacent side to the angle you are looking for and the hypotenuse
tanΘ = opp/adj which is the opposite divided by the adjacent side
Don't forget to take the inverse function to solve for theta.
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Full Member
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Nov 13, 2006, 01:28 PM
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As rudi_in said, the info he gave is for a right triangle, i.e. one with one angle = 90degrees.
If the triangle is not a right triangle things get much more complex. The info at http://en.wikipedia.org/wiki/Triangle is enough to figure it out. If you need someone to give assistance let us know.
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Uber Member
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Nov 19, 2006, 06:48 PM
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Apply the law of cosines first (to find one of the angles), then apply the law of sines to find the other 2.
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New Member
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Nov 11, 2007, 11:26 PM
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Use the Law of Cosines
In any triangle ABC, with sides a, b, and c,
a^2=b^2+c^2-2bc cos A
b^2=a^2+c^2-2ac cos B
c^2=a^2+b^2-2ab cos C
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Junior Member
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Nov 12, 2007, 02:10 AM
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According to the Law of Cosines
In any triangle ABC, with sides a, b, and c,
a^2=b^2+c^2-2bc cos A
b^2=a^2+c^2-2ac cos B
c^2=a^2+b^2-2ab cos C
So if you want find angle A:
From above:
2bc cos A = b^2 + c^2 - a^2
From this equation you can find A
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New Member
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Nov 12, 2007, 04:28 AM
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Originally Posted by DwhiteMann
I how do I find the angles, if I only know the lengths of the 3 sides?
If you know the lengths of the sides and want to find the angle measures of a given triangle, use the law cosines.
Here is link:
The law of cosines. Topics in trigonometry
I hope this helps.
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