How can the frequency with which the direction of a current changes be regulated?

In an inductive circuit, when frequency increases, the circuit current decreases and vice versa.

Explanation:

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west

option number c is the right answer.