Download A. Write the equation of a line given the slope and a point

A. Write the equation of a line given the slope and a point on the line.
Ex) Write an equation of the line that has a slope of –4 and passes through the point (3, –1).
SOLUTION
1. The given line has a slope of m = –4 and passes through the point (3, –1). Use this
information to find the y-intercept. Remember all points are (x, y).
y = mx + b
Write slope-intercept form.
–1 = (–4)(3) + b
Substitute –4 for m, 3 for x, and –1 for y.
–1 = –12 + b
Simplify.
11 = b
Solve for b.
2. Write the equation using slop-intercept form.
y = mx + b
Write slope-intercept form.
y = –4x + 11
Substitute –4 for m and 11 for b to get the equation.
B. Write the equation of the line given two points.
Ex) Write an equation of the line that passes through (−3, 0) and (−1, 6)
SOLUTION
1. Find the slope of the line passing through (−3, 0) and (−1, 6).
Let (x1, y1) = (−3, 0) and (x2, y2) = (−1, 6).
m=
m=
Substitute values.
m=
Simplify.
m=3
Slope is 3.
2. Use one of the given points [either (−3, 0) or (−1, 6)] and the slope you just found and
follow the steps for A above.