# Math Help: Formulas to Remember

09/21/2015

## Math Formulas You Want to Know

As you advance in math, you will find certain operations and concepts will repeat and keep coming up. Here are some formulas that will help you get through your math problems quickly.

### Circle Formulas

The area of a circle is the square of the radius times π. Multiply π times the diameter, or twice the radius, of a circle. When working with arcs, just remember that an arc is a percentage of a circle. Since there are 360 degrees in a circle, first calculate the percentage of the whole circle the arc represents. If the arc is 90 degrees, it is 90/360=1/4 or 25%. Multiply the area or circumference of the whole circle by this percentage to find the area or circumference of the arc.

### SOHCAHTOA

To find the sine, cosine, and tangent of an angle, remember SOHCAHTOA. Sine= Opposite/Hypotenuse Cosine= Adjacent/Hypotenuse Tangent=Opposite/Adjacent Opposite is the side of the triangle directly opposite the angle in question. Adjacent is the side of the triangle next to the angle that is not the hypotenuse. The hypotenuse is the longest side of the triangle. It is also useful to know the reciprocals. Cosecant is the reciprocal of sine= Hypotenuse/Opposite Secant is the reciprocal of cosine= Hypotenuse/Adjacent Cotangent is the reciprocal of tangent= Adjacent/Opposite And finally, the square of an angles sine plus the square of an angle's cosine is 1 and the tangent is the quotient of the sine and cosine.

### Slope Formula

To determine the slope of a line, choose two points on the line and divide the rise (how much the line goes up or down) by the run (how much the line goes left to right).

### Slope-Intercept Formula

In this formula, m is the slope and b is the y-intercept. If you get an equation that is not in this format, you will want to re-write it so that it is. It makes graphing a line much easier.

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