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If $a,b,c$ are the sides of $\Delta ABC$, then $\tan \frac{B-C}{2} \tan \frac{A}{2}$ is equal to

1. $\frac{b+c}{b-c}$
2. $\frac{b-c}{b+c}$
3. $\frac{c-b}{c+b}$
4. none of these

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