Let us mark the points on a graph sheet and call them A, B, C, D and join the four points in the same order to form a four-sided figure.
A = (- 7, 12)
B = (19, 18)
C= (15, - 6)
D= (- 11, - 12)
We know that slope of a line is given by
Slopes of lines AB, BC, CD and DA are calculated as given below.
We see that slope of AB = Slope of CD
Slope of BC = Slope of DA
So AB ∥ CD and BC ∥ DA
ABCD is a parallelogram.
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