Starting with tanAtan(A−B)+sin2Asin2C=1, rearrange to tanAtan(A−B)=1−sin2Asin2C.
⇒tan(A−B)tanA=sin2A−sin2C.
Applying the identity sin2θ=1+tan2θtan2θ and simplifying leads to a relationship between the tangent values.
The constraint reduces to (tanC)2=tanA⋅tanB, which means tanA, tanC, and tanB form a geometric progression with common ratio r=tanAtanC.