Q : if $\displaystyle Cos B / a = Cos A / b$

Prove that : $\displaystyle a=b$ and $\displaystyle c^2$$\displaystyle =$$\displaystyle a^2$$\displaystyle +$$\displaystyle b^2$

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- Sep 6th 2011, 12:19 PMmido22Cosine law
Q : if $\displaystyle Cos B / a = Cos A / b$

Prove that : $\displaystyle a=b$ and $\displaystyle c^2$$\displaystyle =$$\displaystyle a^2$$\displaystyle +$$\displaystyle b^2$ - Sep 6th 2011, 11:27 PMOpalgRe: want help in cosine law
What have you tried? You could start by using the cosine rule to express cos A and cos B in terms of a, b and c. Then try to simplify the resulting equation.

**Edit.**After checking the question, I think that you have stated it wrongly. It should say

Prove that : $\displaystyle a=b$**or**$\displaystyle c^2=a^2+b^2$. - Sep 7th 2011, 03:08 PMmido22Re: want help in cosine law
yes it is or not and i made alot of tries but all reach to same result :

$\displaystyle b^2$$\displaystyle ($$\displaystyle c^2$$\displaystyle -$$\displaystyle b^2$$\displaystyle ) =$$\displaystyle a^2$$\displaystyle ($$\displaystyle c^2$$\displaystyle -$$\displaystyle a^2$$\displaystyle )$ - Sep 7th 2011, 03:25 PMpickslidesRe: want help in cosine law
- Sep 7th 2011, 03:35 PMmido22Re: want help in cosine law
no i can't say so becz a!=b

- Sep 7th 2011, 04:22 PMskeeterRe: want help in cosine law
- Sep 7th 2011, 04:25 PMmido22Re: want help in cosine law
and how can i get a=b from same problem