Linear Functions for Kids: Graph y = mx + b Using Slope and Intercept (Grade 8 Math)

Hi, I'm Luna from DoodleBeez. Today we are learning about linear functions. A linear function makes a straight line when we graph it. We can write it as y equals m x plus b.

In y equals m x plus b, the letter m is the slope. It tells us how steep the line is. The letter b is the y intercept. It is where the line crosses the y axis.

Let's try y equals two x plus one. When x is zero, y is one. When x is one, y is three. When x is two, y is five. Each time x goes up by one, y goes up by two. That is the slope.

To graph it, start at the y intercept, which is the point zero, one. Then use the slope. Go right one and up two, and plot a point. Repeat, then join the points with a straight line.

If the slope is negative, the line goes down from left to right. For y equals negative three x plus four, start at four on the y axis. Then go right one and down three each time.

We can also write the equation from a table. Here, y is five when x is zero, so b is five. Each step, y grows by four, so m is four. The function is y equals four x plus five.

Now it's your turn. A plant is three centimeters tall and grows two centimeters each week. Write a function for its height y after x weeks. Pause and try. It starts at three and grows by two, so y equals two x plus three.

Great job! Remember, in y equals m x plus b, m is the slope and b is the y intercept. Start at b, then use the slope. Practice linear functions in Middle School Math at doodlebeez.com. See you next time!