Q: Theta or Phi? When do I use theta to find the angel and when do I use phi to find the angle for a vector?
A: Theta and Phi are defined as the angles of vector versus different axes, depending on the diagram in problems. Theta is the most popular angle of vector versus the x-axis (positive x direction). As a result, Ax = A cos(theta) and Ay = A sin(theta) for vector A.
