Slope-intercept form: y = mx + b [m is the slope, b is the y-intercept or the y value when x = 0 ---> (0, y) or the point where the line crosses through the y-axis]
For a line to be perpendicular to another line, the slope has to be the negative reciprocal of the original line's slope.
For example:
Slope(m) =
Perpendicular line's slope: or -2 [positive to negative]
m = or -3
Perpendicular line's slope: [negative to positive]
y = -x + 3
m = -1 So the perpendicular line's slope is 1, now plug it into the equation
y = mx + b
y = x + b To find b, plug in the point (3, 1) into the equation
1 = 3 + b Subtract 3 on both sides to get b by itself
1 - 3 = 3 - 3 + b
-2 = b The y-intercept is -2