Lessons

These lessons cover everything you need to find the slope of a line and write its equation. Each one has worked examples, and most link to the Slope Finder so you can see the example on a graph and move the points yourself.

Start here

1. What is slope? What slope measures, and positive, negative, zero and undefined slopes.
2. The slope formula: m = (y₂ − y₁) / (x₂ − x₁), and how to avoid sign mistakes.
3. Zero and undefined slope: horizontal and vertical lines.

Equations of a line

1. Slope-intercept form: y = mx + b, the most common form.
2. Point-slope form: y − y₁ = m(x − x₁), for when you know one point and the slope.
3. Standard form: Ax + By = C, and converting between forms.

Using slope

1. Finding the equation of a line from a graph
2. Finding slope from a table of values
3. Parallel and perpendicular lines
4. Practice problems with answers

Two lines at once: systems of equations

1. Solving systems of equations by graphing: the solution is where the lines cross.
2. The substitution method: make one variable the subject and substitute it.
3. The elimination method: add or subtract the equations to remove a variable.
4. No solution or infinitely many solutions: parallel lines and identical lines.
5. Systems of equations word problems: tickets, phone plans and more.

To check any system, use the Intersection Finder.

Quadratics with lines

1. Solving quadratic equations by intersecting lines: rearrange to x² = mx + k and find where the line meets y = x².

Try it with the Quadratic Solver.