A 2d shear looks like [[1,a],[0,1]] and a rotation of q is [[cos q, -sin q],[sin q, cos q]] So you have a system like this to solve: [[1,a],[0,1]]*[[1,0],

A 2d shear looks like [[1,a],[0,1]] and a rotation of q is [[cos q, -sin q],[sin q, cos q]] So you have a system like this to solve: [[1,a],[0,1]]*[[1,0],[b,1]]*[[1,c],[0,1]] == [[cos q, -sin q],[sin q, cos q]] It's not hard to solve (despite being overdetermined) and you can even throw that line above into a CAS directly. The solution is a bit long to paste here though.