Question

In right ∆ABC, C is a right angle and sin A = 243/312. What is mB?

Answer 1

The sin of any given angle is:
sin(∅) = perpendicular / hypotenuse

The perpendicular of angle A will be equivalent to the base of angle B. Therefore,
Cos(B) = 243/312
B = Cos⁻¹(243/312)
B = 38.8°

The measure of angle B is 38.8 degrees.