I'm going to point significantly (*points significantly*) to my signature. The clue is given by tiny-tim (and that is what they want you to use): make a diagram of a right triangle with x as one of the non-right angles and use v, written as v/1 , as the ratio of the sides that would come from finding the tangent of angle x (label the sides of the triangle appropriately).
Now, in the same triangle, what angle has a tangent of 1/v ? What is the relationship between that angle and angle x ?
(And, with all due respect to mhill, while that relationship is true, the math is probably way beyond what is being done in Calixto's course...)