Right Triangles
Every right triangle has an interior angle of 90°. The other two angles have a mesure of less than 90°, i.e. they are acute.
The side that is in front or opposite to the right angles is called the hypotenuse, and the other two sides are the legs.
Every acute angle of the triangle has an adjacent leg, an opposite leg and the hypotenuse that is always adjacent.
The given angle of 63° has 16 as its opposite side and has x as the hypotenuse, thus:
The side length of 16 is opposite to the angle of 63°.
The side length of x is the hypotenuse of the triangle.