Unlike the SAT, the ACT does not give you a list of formulas at the beginning of the math test. And that means there are some you absolutely need to have memorized. Here are the more common ones that you might be called upon to use that you should definitely know by heart:

## Averages:

S=AT

You may be more familiar with this as Average = Sum/Things, but on both the SAT and the ACT, you will more often find that the test will give you the average and ask you to find the sum, and this variation of the equation makes that easier. So that’s why I like using the mnemonic SAT to remember the formula.

## Slope:

You can bet you’ll be asked to find the slope in at least one ACT problem. If you are given two points, or can find two points on a graph, you simply take the y value of one point and subtract the y value of the second and then divide that by the difference between the corresponding x values (see above). Make sure you don’t mix them up–this is the most common mistake students make!

If you are given an equation, make sure the equation is in slope-intercept form (y=mx+b) and whatever the value is before the x (m in our equation) is your slope.

## Circumference of a circle

C=2πr

Area of a circle

A=πr2

A lot of people get these two equations confused because they are so similar. Remember, the squared value goes with the area. To remember this, you can think about finding the area of an actual square. The area of a square is the length of one of its sides “squared” (s2), so remember that with circles as well, the squared value goes with area.

## Volume of a cylinder

V=πr2h

The way I remember this one is to recall that a cylinder is just a flat circle that’s been stretched out. So we take the area of that circle, and then stretch it out by multiplying it by the height.

## SOHCAHTOA

This one is more of a mnemonic than a formula. But if you don’t know anything else about trigonometry, this one is crucial. It might help you to write it out every time you see a right triangle trig problem, so that you don’t mix it up.

SOHCAHTOA helps you remember that:

Sine=opposite/hypotenuse

For a full list of formulas to know for the ACT, including some more advanced ones, check out this handy-dandy list we’ve made for you here!

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Kristin makes sure Magoosh's sites are full of awesome, free resources that can be found by students prepping for standardized tests. With a PhD from UC Irvine and degrees in Education and English, she’s been working in education since 2004 and has helped students prepare for standardized tests, as well as college and graduate school admissions, since 2007. She enjoys the agony and bliss of train running, backpacking, hot yoga, and esoteric knowledge.

### 2 Responses to “ACT Math Tips: Must-Know Math Formulas for the ACT”

1. Mohammed says:

I love your videos. They helped me alot. Best preps ever!!

• Kristin Fracchia says: