Theory:

The hypotenuse and one side (base or perpendicular side) of a right-angled triangle are respectively equal to the hypotenuse and one side of another right-angled triangle, and then the triangles are congruent.
Suppose the two right triangles with the first triangle of  hypotenuse \(a\) units and one side (either base or perpendicular) of \(b\) units which are congruent to the second triangle whose hypotenuse is the same \(a\) units and one side (either base or perpendicular) measure the \(b\) units.
Example:
Theory_1.1_1.png
In here the two right triangles with the first triangle of  hypotenuse \(10 cm\) and one side (base) of \(8 cm\) which are congruent to the second triangle whose hypotenuse is the same \(10 cm\) and one side (base) measures the \(8 cm\).  Thus, the triangles \(ABC\) is congruent to \(PQR\).  In symbolic form, \(ABC\)  \(PQR\).
Important!
RHS stands for "right angle, hypotenuse, side" and means that we have two right triangles with hypotenuse and one side are equal.