When labelling a length as the opposite, it can be shortened to 𝒐. (\ (o\)) side, and the adjacent close adjacentThe side of a right-angled triangle between the right-angle and the angle mentioned.

For two right-angled triangles, if an angle (other than the right angle) is the same, the third angle will also be the same. This is true because angles in a triangle add up to 180°.