Relation between area of a triangle on a sphere and plane We know area of a plane triangle $\Delta=\sqrt{s(s-a)(s-b)(s-c)}$ where $s=\frac{a+b+c}{2}$.
I was just thinking: let we have a triangle with arc length $a,b,c$ on a sphere of radius $r$, do we have any similar kind of formula for that spherical triangle?  when radius of $r\to \infty$ we get the plane, so do we have any estimate of area of spherical triangle when $r\to\infty$?
Any reference and article link are also welcome! Thank you.


Source: This Dr. Math Article

Novice here, so please excuse any mistakes. The ratio should be:
$$
\frac{ 180 \cdot \sqrt{ s(s-a)(s-b)(s-c) } }
{ 4 \cdot \pi  \cdot R^2 \cdot \arctan \left(
\sqrt{ \tan \left( \frac{s}{2} \right) \cdot \tan \left( \frac{s-a}{2} \right) \cdot \tan \left( \frac{s-b}{2} \right) \cdot \tan \left( \frac{s-c}{2} \right) }
\right) } $$
Still needs some simplification, though...
Basically, I just placed Heron's formula for the area of planar $\Delta$s above the $\frac{ \pi \cdot R^2 \cdot E}{180}$ formula for the area of a spherical $\Delta$. Since I didn't have the angular measures required to calculate $E$, I used this formula:
$$ \tan \left( \frac{E}{4} \right) = \sqrt{ \tan \left( \frac{s}{2} \right) \cdot \tan \left( \frac{s-a}{2} \right) \cdot \tan \left( \frac{s-b}{2} \right) \cdot \tan \left( \frac{s-c}{2} \right) } $$
