The area of a spherical triangle (sphere radius $a$ ) is given by spherical deficit $ (A+B+C-\pi)$ times $ a^2 $ when enclosed between great circular arcs.
If tangential curvature radii are $ Rg_a, Rg_b, Rg_c$ what is the area of the spherical triangle enclosed between small circles? Positive if apex angle reduces with respect to a geodesic.
