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Perpendicular Lines Investigation Group C

Two lines are perpendicular to each other if they intersect each other at 90 degrees.  Is there any relationship between the gradients of perpendicular lines?

1

1

The diagram above show two lines which are perpendicular to each other. The lines are y = x +2 and y = -x + 2. What is the gradient of Line 1? What is the gradient of Line 2?

2

The Geogebra Applet shows two perpendicular lines and the gradients (slopes) of these lines. Drag the blue point to get different sets of perpendicular lines. Jot down the gradients of 4 sets you try. Eg. Set 1 : m1=?, m2=? Set 2 : m1=?, m2=?

Conclusion : The lines y = m1x + c1 and y = m2x + c2 are perpendicular if and only if ______________________________.