The angle between two rays in 3D space This is a problem from Mathematics GRE Subject Test - #42.

In the xyz-space, what is the degree measure of the angle between the rays $z= (x>=0), y=0$ and $z=  (y>=0), x=0$?
a)0; b)30; c)45; d)60; e)90

My Attempt at a Solution
Because the first set of rays are always along the line y=0, they must be spread out on solely the x-z plane, in the direction of the positive x-axis.
Similarly, the second set of rays would be on the y-z plane, and in the direction of the positive y axis. So I figured that because the rays are on perpendicular planes, they should have an angle of 90 degrees.
Sorry if this is drastically wrong, I'm at a loss where to proceed. I'm not totally even sure what topic to tag this under. Any help is much appreciated. Thanks

Well, this might not be kosher but:
o = (0, 0, 0) is the vertex of the two rays.  Let a = (1,0,1) is in Ray 1. Let b = (0, 1,1) by in ray two.  The distance between a and o is $\sqrt{2}$. Between b and o is  $\sqrt{2}$ and between a and b is $\sqrt{2}$.  So the three points form an equilateral triangle.  So the angle is 60 degrees.
