Description: Sal demonstrates how to write the equation of several lines when given their graphs. So you may or may not already know that any linear equation can be written in the form y is equal to mx plus b. If you get x is equal to 0, remember x is equal to 0, that means that's where we're going to intercept at the y-axis. If x is equal to 0, this equation becomes y is equal to m times 0 plus b.*Teacher Advisor is 100% free.