A [i]shear[/i] is a transformation of the plane that preserves straight lines and areas, but not angles.[br]A shear doesn’t move points along a line (its axis), and moves other points along lines parallel to the axis by an amount proportional to their distance from the axis (its shear factor).[br]The matrix of a shear whose axis is the x axis with shear factor [i]a[/i] is [img]blob:https://www.geogebra.org/516cae9c-5d3b-4a00-803e-0ab139076209[/img], or [code]{{1,a},{0,1}}[/code] in GeoGebra code.[br][br]The reason areas are preserved come from Euclid: parallelograms on the same base and with the same height have the same area.