In the given right triangle ABC, right angled at B, the hypotenuse, base and perpendicular with respect to ϕ are given by -
A)AC
B)BC
C)AB
The hypotenuse is the side opposite to the right angle, which is AC here. The base is the horizontal side adjacent to the right angle, i.e., BC and the perpendicular is the side perpendicular to BC, i.e., AB.