# Formulas Worth Memorizing

Some formulas, those worth memorizing, occur frequently when you’re doing algebraic manipulations and working through mathematical applications. You’ll find ways to use these formulas even when you’re doing something other than algebra, such as planning a garden or road trip. Of course, you need to know what the letters and symbols in the formula mean, so the list here shows both the formulas and the explanations.

*d* = *rt*

The distance traveled, *d*, equals the rate, *r*, multiplied by the time, *t*.

*I = Prt*

Simple interest earned, *I*, equals the principal, *P*, times the interest rate in years, *r *(as a decimal), times the time, *t *(in years).

The amount, *A*, resulting from compounding interest equals the principal, *P*, times the sum of 1 and the quotient of the rate of interest, *r*, divided by the number of times compounded each year, *t*, all raised to the product of the number of times compounded, *n*, times the term (number of years), *t*.

The temperature in degrees Fahrenheit, *F*, equals 9/5 time the degrees Celsius, C, plus 32.

*a*^{2} + *b*^{2} = *c*^{2}

The Pythagorean Theorem shows the relationship between the sides of a right triangle. The longest side, measuring *c*, is always opposite the right angle. The sides measuring *a* and *b* are the other two sides.

The solutions of a quadratic equation, *ax*^{2} + *bx* + *c* = 0, are found by substituting the values of *a*, *b*, and *c* into the formula.