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Shear N first

Here shear N (with a slanting invariant line through D) is applied to square ABCD.

What shape and size is the resulting image?

How far have points A, B and C moved?
What are their distances from the invariant line n?
What is the shear factor of shear N?

On the next page we apply a shear P to the image, which produces the same size rectangle as M-then-N.
What can you say about the invariant line for P, and what is the shear factor?