Question 650170
first, a slope for (1.-1), (4,1)

*[invoke slope 1, -1, 4, 1]


next, a slope for (2,2), and (5,4)

*[invoke slope 2, 2, 5, 4]

lines have same slope; s0, they are parallel

next, a slope for (1.-1), and (2,2)

*[invoke slope 1, -1, 2, 2]

and, a slope for (1.-1), and (2,2)

*[invoke slope 4, 1, 5, 4]

lines have same slope; s0, they are parallel

if both pairs of sides are parallel, then you can conclude that those four points define the {{{vertex}}}{{{ points}}} of a {{{parallelogram}}}


{{{ graph( 600, 600, -6, 10, -6, 10, 0.67x-1.67, 3x-11, 3x-4,0.67x+1.65 ) }}}

as you can see, their intersection is a {{{parallelogram}}}