Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

I'm facing a problem. We have lengths of 3 segments. How to see if the triangle built of our 3 segments has a specific angle, for example 60°?

share|improve this question

2 Answers 2

up vote 1 down vote accepted

The law of cosines says that $$c^2=a^2+b^2-2ab\cos\gamma.$$ Thus $\gamma=60^\circ$ iff $$c^2=a^2+b^2-ab$$ (or with the sides permuted for the other angles).

share|improve this answer
    
Thanks ;) I've forgotten that helpful law ;) –  enedil Feb 6 at 21:32

To find each specific angle, use the law of cosines:

$$c^2 = a^2 + b^2 - 2ab \cos C$$

Where $a, b, c$ are side lengths and $A, B, C$ are the angles opposite their corresponding sides.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.