Learning Resources

Investigation 3: Parallel and Perpendicular Lines

Test yourself (solution)

First sketch the points on a grid.

Then use the slope formula to find the slopes of the four sides:

From the calculations we can see that the slopes of  CD and FE are equal and therefore CD || FE . However, the slopes of the other two sides are not equal, so they are not parallel. A quadrilateral with only one pair of opposite sides parallel is called a trapezoid, so CDFE is a trapezoid.

The slopes of CD and EC are negative reciprocals of each other (their product is -1), so Ð ECD is a right angle. Also the slopes FE and EC are negative reciprocals of each other, so Ð CEF is a right angle.