# A problem in Trigonometry (Properties of Triangles)

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1. May 11, 2017

### Wrichik Basu

• Member warned that the homework template must be used, and an effort shown
In any triangle ABC, prove that $$(b+c-a) \left( \cot {\frac {B}{2}} + \cot {\frac {C}{2}} \right)=2a \cot {\frac {A}{2}}$$

2. May 11, 2017

### Buffu

Did you try to solve this ?
Also you should not vandalise the template.

3. May 11, 2017

### Wrichik Basu

I tried in several ways, trying to change a, b, c to 2R sin A and like that, or trying the formulae for cot A/2, but got nowhere.

4. May 11, 2017

### Buffu

Use sine rule and A + B + C = 180.