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!