Right Spherical Triangle

Case of the Right spherical triangle: Right at $C$ .
If the triangle has more than one interior angle with a value of $90^{\circ}$ , it is said to be oblique.

The Napier’s Circle:

In the right triangle, the sides and angles are written in a consecutive way but without the right angle itself while taking the complementary angles for the quantities opposite to the right angle.

From the graph:
$\bar{B}=90^{\circ}-B$
$\bar{A}=90^{\circ}-A$

$\bar{c}=90^{\circ}-c$

Sine rule for opposite parts:
The sine of any middle part is equal to the product of the cosines of its opposite parts.
Example:
$\sin {a}=\cos {\bar{c}}\cos {\bar{A}}$
$\sin {a}=\cos {(90^{\circ}-c)}\cos {(90^{\circ}-A)}$
This gives:
$\sin {a}=\sin {c} \sin {A}$