Given sin (-∅) = -1/4 and tan∅ = √15/15.
What is the value of cos∅?

Cos (theta) would be equal to 15/-1!

The reason is because the inverse of sin is equal to the hypotenuse over the opposite angle, meaning the hypotenuse would be -1. Tan is equal to the opposite over the adjacent angle, meaning the adjacent angle equals 15. Cos is equal to the adjacent over the hypotenuse, making cos (theta)= 15/-1!