$phi = arccos( v_x / |vecv| )$

Enter a value for all fields

This equation computes the angle, $phi$ of a vector from the magnitude of the angle, | $vecv$ | and the x-component of the vector, $v_x$ . See Figure B. /attachments/1dde17ed-881f-11e4-a9fb-bc764e2038f2/Vector x-y components.png

Reference

Young, Hugh and Freeman, Roger. University Physics With Modern Physics. Addison-Wesley, 2008. 12th Edition, (ISBN-13: 978-0321500625 ISBN-10: 0321500628 ) Pg 16 eq 1.6