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

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

Postby mitnord » Wed Mar 04, 2009 8:37 pm

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.

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stapel_eliz
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Postby stapel_eliz » Wed Mar 04, 2009 9:28 pm

mitnord wrote: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.

mitnord wrote: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.

If you get stuck, please reply showing your steps and reasoning. Thank you! :D


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