## The equation of the line L through D perp. to side AB

Quadratic equations and inequalities, variation equations, function notation, systems of equations, etc.
mitnord
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Joined: Mon Feb 23, 2009 11:17 pm
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### The equation of the line L through D perp. to side AB

The triangle has the following coordinates: A(-14, 11), B(3, 4) and C(10, 11)

Point D is the middle of the side AB.

Line l goes through the point D is perpendicular to the side AB.

How to find the equation of the line l.

Thanks.

Note: we've just had vectors, can't figure out how to solve.

stapel_eliz
Posts: 1628
Joined: Mon Dec 08, 2008 4:22 pm
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The triangle has the following coordinates: A(-14, 11), B(3, 4) and C(10, 11)

Point D is the middle of the side AB.
Plug the coordinates of A and B into the Midpoint Formula to find the point D in the "middle" of side AB.
Line l goes through the point D is perpendicular to the side AB.

How to find the equation of the line l.
Plug the coordinates of A and B into the slope formula to find the slope of the line through A and B. Then remember that the perpendicular slope is the negative reciprocal (you flip the old slope, and change the sign).

Now that you have the coordinates of D and the slope of the perpendicular line, plug these into one of the straight-line equations, such as the point-slope formula.