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Finding the Equation of a Graphed Line - Problem 3 2,862 views

Teacher/Instructor Alissa Fong
Alissa Fong

MA, Stanford University
Teaching in the San Francisco Bay Area

Alissa is currently a teacher in the San Francisco Bay Area and Brightstorm users love her clear, concise explanations of tough concepts

To write the equation of a horizontal or vertical line, think about what points the line contains. In horizontal lines, all the coordinates have the same y values, so the equation of the line is y = [value]. In vertical lines, all the coordinates have the same x value, so the equation of the line is x = [value].

Some people don't like Math because they feel like it tons and tons of memorizing. And you guys I understand where you are coming from a lot of the times there are little things that you have to memorize. However that happens really rarely and to be honest most of the time in Math you can figure things out if you can remember definitions and acute foundational ideas.

So one thing that students might choose to memorize, but again you don't have to, is how to write the equations for vertical and horizontal lines. Like in this problem I have a line 1 which is a horizontal line and line 2 which is a vertical line.

Some students have it memorized that horizontal lines always have the equation y equals some constant. So I could use that idea to figure out that's going to be y equals 2. Let's say you didn't have that memorized, one way you might figure out the equation of that line is by thinking about what points that line contains.

For example this line goes through the point 0 for x, 2 for y, it goes through 1 for x, 2 for y (2,2) and you could see a pattern and all those points my value is always 2. So if you didn't have this memorized you could try using points and see okay y is always equal to 2. No matter what x is my y value stays at that constant value 2.

The same idea applies to vertical lines like this one here. I can see a few points where I have x is -5 y is -1, x is -5 y is negative whatever that is 3 I think, following this pattern I can see my x value is always -5. So you could memorize that horizontal, excuse me, vertical lines always have the equation x equals some constant or you could go through and be able to find it using logic. My x value is always -5 for all the points at that vertical line goes through.

So you guys if you're not good memorizers that's totally fine you can still be successful in your Math classes but you are going to have to remember some logic tricks like this to help you figure out the equations for vertical and horizontal lines.