There are several situation in which it's necessary to ascertain, or set, the slope of the line represented by a linear equation. This is needed in problems involving the number of solutions to a system of linear equations, because a system with lines having different slopes have exactly one solution, and a system with lines that have the same slopes either have no solutions (if the lines' y-intercepts are different, so the lines are parallel and distinct) or the system has an infinite number of solutions (if the lines' y-intercepts are the same, so the lines are identical). The slope is also involved in problems that contain perpendicular lines, because the slopes of perpendicular lines are the negative reciprocals of each other.

When a line is in slope-intercept form (y = mx + b), the slope is directly represented by the coefficient m of the variable x. For standard form (Ax + By = C), you can calculate the slope by using the formula -A / B (we never remember this, so we just solve for y and look at the x-coefficient). Other forms of linear equation either expose the slope directly or require some calculation or manipulation to ascertain it, and the most generalized form with collected like terms on each side, Ax + By + C = Dx + Ey + F, requires a fair bit of algebra to get the slope out of it, though an equation of that form is unlikely to appear on the digital SAT.

Desmos does not provide a built-in generalized facility for giving you the slope of a linear equation in any form. However, mostly to satisfy our curiosity, we've developed a technique that will extract that information. The method is sufficiently involved that it is likely to be impractical in most situations, so we are not urging students to memorize this approach. Nonetheless, you might find it interesting. It does involve a basic principle of calculus (<runs screaming from the room>), but we suggest taking a look at the approach in the walkthrough contained in the demonstration graph below. To summarize, we define a function named Slope() that uses differentiation to ascertain the slope of an equation given the expressions on each side of the equation; it looks like this; l and r represent the expressions on the left and right sides of the equation, respectively (though it doesn't matter which you use for which, as equations are symmetrical):

See the graph below for further explanation and a demonistration.