# Rotating a vector 90degrees

1. Oct 16, 2012

### sparkzbarca

This isn't actually a homework question, i'm programming something, it's just what should be fairly simple math i'm just not certain how to do it.

Assume I have a normalized vector which points directly up {0,1,0}.

I also have another vector X.

I'd like to rotate vector X along the

crossmultiply(up,vector x) axis
(i know how to cross multiply)

90 degrees towards {0,1,0}

but basically i'd no idea how to convert vectors to angles or maybe I need to use radians,
if it helps the axis and the up can be normalized so that it can be assumed your working on the unit circle if that makes it easier to find.

If you could help me or even just point me to a web resource that helps that'd be appreciated, i tried looking up vectors to angles but didn't really seem to get anywhere.

2. Oct 16, 2012

### Staff: Mentor

???
I don't know what you mean by this. You don't rotate a vector along an axis - you rotate it around some vector.
You can use a rotation matrix to rotate a vector. See the wiki article, http://en.wikipedia.org/wiki/Rotation_matrix.

3. Oct 16, 2012

### sparkzbarca

Oh i understand a vector rotates around another vector but to me at least axis is short for the vector around which something rotates. I believe I solved the dilemma but thank you!