A triangle has vertices P (6, 7), Q(2 -1) and R(-2, 1). How do I use the slopes of the sides to show that PQR is right angled.

Printable View

- Oct 30th 2008, 03:47 PMmattyanalytic geometry triangle
A triangle has vertices P (6, 7), Q(2 -1) and R(-2, 1). How do I use the slopes of the sides to show that PQR is right angled.

- Oct 30th 2008, 03:49 PMmasters
- Oct 30th 2008, 03:51 PMKhaali91
Use the equation

__y2-y1__

x2-x1

to find the slopes of the lines connecting the points...

the slopes that are negative reciprocals are the 90 degree angle because it makes a perpendicular line - Oct 30th 2008, 03:53 PMBoboStrategyTriangles
Two lines are perpendicular if their slopes are negative reciprocals.

The slope of the line between (-2, 1) and (2, -1) is:

(1 - (-1)) / (-2 - 2) = 2 / -4 = -1/2

The slope of one of the other lines is 2. (your job to figure out which one)

Those two lines are negative reciprocals - so they are perpendicular.

So the triangle is a right triangle.