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zorro
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Homework Statement
In a triangle ABC, a=6 b=3 cos(A-B)=4/5. Find the angle C.
Homework Equations
The Attempt at a Solution
here we need to find tan(A-B/2)
I used the formula tan2x=2tanx/(1/tan^2x)
and got 2 values of tan(A-B/2) as -3 and 1/3
On what explanation do I reject one of them?
-90<A-B/2 <90
so tanA-B/2 can be both positive and negative.
Please explain in detail