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# perpendicular lines watch

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1. A = 4,3
B = 2,2
C = 5,-4

Show that the lines AB and BC are perpendicular.

How do i do this? Do i just draw a graph or is there an equation?
2. (Original post by caitlindavies)
A = 4,3
B = 2,2
C = 5,-4

Show that the lines AB and BC are perpendicular.

How do i do this? Do i just draw a graph or is there an equation?
3. there is a simple test to see if two gradients belong to perpendicular lines.
4. (Original post by 16Characters....)
nothing...all i know is they are right angles
5. (Original post by caitlindavies)
nothing...all i know is they are right angles
The gradients of two perpendicular lines multiply together to get -1.

Alternatively you can draw a diagram and use the converse of Pythagoras' theorem to prove that the angle made by AB and BC is a right angle.
6. Find the gradients of both lines by using (y2-y1)/(x2-x1).

Then multiply the gradients of the two lines, if the product is -1 then the lines are perpendicular.

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Updated: October 18, 2015
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