Folks,

I am struggling to understand how the attached expressions were obtained for the simple rotation of 2 axes normal to each other by an angle $\displaystyle \theta$

This is different to what is shown the wiki link Rotation matrix - Wikipedia, the free encyclopedia (See in 'two dimensions')

Ie, $\displaystyle x'= x\cos \theta - y \sin \theta$ and $\displaystyle y'=x \sin \theta + y \cos \theta$

Any clues?

Regards

bugatti