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# Matrix/ geometrical transformation watch

If T rotates each point through an angle theta about the x-axis in the direction that moves the point (0,0,1) towards the point (0,-1,0), find the matrices representing the geometrical transformation
T:R^3 ->R^3 with respect to the standard basis.

Any help would be greatly appreciated!
2. Hmm .. you're not getting many takers, so I'll try

Rotation matrix in 2D is easy

You really have a 2D problem here.

Isn't it just a question of padding out some 2D rotation matrix to make it a 3D one?
3. I'm not sure, how would you do that anyway? All we're given about anticlockwise transformation in 2d is just
(cosx -sinx)
(sinx cosx) I'm not sure how to apply that in 3d...

My understanding is just to work out whether T is an anticlockwise or clockwise transformation, but surely it could be either depending on which way you look at it?
4. Well, I think the x co-ordinate is unchanged by the rotation. So we're looking for a matrix of the form (1,0,0/0,?,?/0,?,?)

If you just considered the y and z co-ordinates as a 2D problem, would you be able to construct that rotation matrix?

And if you were worried about clockwise/anti-clock, you could always just try the numbers?
5. Thank you, that's actually quite helpful!

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