### 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:
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, $$ABC$$ $\cong$ $$PQR$$.
Important!
RHS stands for "right angle, hypotenuse, side" and means that we have two right triangles with hypotenuse and one side are equal.