How do we know that theta will be in clockwise and anticlockwise in tan(phi-theta) - Maths - Trigonometric Functions

Question

How do we know that theta will be in clockwise and anticlockwise in
tan(phi-theta)?

Darsh · Accepted Answer

If there is negative sign with theta only then theta will be
clockwise otherwise anticlockwise

How do we know that theta will be in clockwise and anticlockwise in tan(phi-theta)?