trigonometry

Question: In triangle $ABC,$ $\frac{1+\cos (A-B)\cos C}{1+\cos (A-C)\cos B}=$

1) $\frac{a-b}{a-c}$

2) $\frac{a+b}{a+c}$

3) $\frac{{{a}^{2}}-{{b}^{2}}}{{{a}^{2}}-{{c}^{2}}}$

4) $\frac{{{a}^{2}}+{{b}^{2}}}{{{a}^{2}}+{{c}^{2}}}$

Solution:

Explanation: No Explanation

Relation between sides and angles Solutions of triangles

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