Lines and slope

Once you can solve an equation, the next step is seeing what an equation looks like. A linear equation in x and y draws a straight line, and two numbers describe that line completely: how steep it is and where it crosses the y-axis. This topic is about reading and using those two numbers. You begin with slope, the change in y divided by the change in x, where the usual slip is subtracting the points in a different order on the top and the bottom. Next comes slope-intercept form, y = mx + b, and how to pick out m and b even when the equation is rearranged. Then you graph a line straight from its equation, starting at the intercept and stepping by the slope. The topic finishes with systems of equations, where two lines meet at one point and substitution finds it. Each page shows the common mistake, a guided example and three questions to check yourself.