First find the slope of the line DM using the slope formula: [tex]\frac{y_2-y_1}{x_2-x_1}[/tex].
Use the points D(0, 2) and M(-3, -5). Substitute in -5 for y2, 2 for y1, -3 for x2, and 0 for x1.
[tex]\frac{-5-2}{-3-0}[/tex], subtract the coordinate points.
[tex]\frac{-7}{-3}[/tex] = [tex]\frac{7}{3}[/tex]; the slope of the line DM is 7/3.
Perpendicular lines have opposite reciprocal slopes, meaning you switch the sign (say for example a negative becomes a positive, a positive becomes a negative) and you flip the fraction over (for example 1/2 becomes 2/1 and 2/1 becomes 1/2).
The opposite reciprocal of 7/3 is -3/7, so the line perpendicular to the line DM has a slope of -3/7.
