Describing a Shear requires 2 things;
a) the invariant line, and
b) the shear factor.
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Drag the points k, A, B or C and observe 

• how the image of A, B and C changes under different shear factors?
• how the image of A, B and C changes as A, B and C moves away from the invariant line?
• what happens if A, B or C is on the invariant line?
• how shear factor is calculated?  
• area of both object and image.