# ACT Math: Coordinate Geometry

## SAT Question of the Day

The SAT question of the day is a Sentence Completion Question that has already been addressed on this blog: click here to see an explanation.

## ACT Question of the Day

The ACT question of the day is a math question that tests your knowledge of coordinate geometry.  You must choose the graph that most accurately depicts the line y = 3x + 1.  Many students will graph this on a calculator, but you should be able to select the answer in just a couple of seconds by relying on your knowledge of the equation of a line.

The equation of any line can be written as y = mx + b.  The m is the slope of the line.  Your slope (3) is positive, so you know that the line must also be positive; it must start out low and increase. That means that you can eliminate answer choices (D) and (E) because they are negative; they start out high and decrease.

Then look back at your equation. In y = mx + b, the variable b represents the y-intercept, where the line crosses the y-axis.  Your line, y = 3x + 1, will cross the y-axis at 1.  You can eliminate answer choice (A) because this line passes through the origin, (0,0).  You can eliminate (B) because this line crosses the y-axis under the origin and would have a negative value for b.  You have eliminated all but one choice.