How to Do Factorials on a Scientific Calculator

••• Yozayo/iStock/GettyImages

Scientific calculators simplify the process of inputting and calculating more complicated expressions than standard calculators. Ordinary calculators can handle factorials, but you have to enter them manually, and this can be time-consuming if you’re taking the factorial of a bigger number. Scientific calculators make this much easier, with most of them including a “x!” key purpose-built for evaluating factorials. All you have to do is enter the number you want to take the factorial of and then press this key to evaluate it.

TL;DR (Too Long; Didn't Read)

Find the factorial of a number on a scientific calculator, enter the number and press the “x!” key. This may require you to press “shift,” “2nd” or “alpha” first depending on your model of calculator and the location of the symbol. Press “=” to get the result.

What Is a Factorial?

Factorial is the name given to the process of multiplying together all of the integers up to a certain number. So 5 factorial is 1 × 2 × 3 × 4 × 5 = 120 and 3 factorial is 1 × 2 × 3 = 6. Notice that a small increase in the number you’re taking a factorial of can lead to much bigger answers. The symbol for a factorial is x!, where x is the number you want to take the factorial of. For 4! you can say “four factorial,” though you may also hear the occasional “four bang” or even “four shriek.”

Factorials on a Scientific Calculator

Scientific calculators make easy work of evaluating factorials. The specific process depends on the model of calculator you have, but generally you need to look for the “x!” key on the calculator to complete the operation. First, press the number you want to take the factorial of, press the “x!” key, and finally press the “=” key to evaluate it.

Finding the “x!” key on your calculator will be the most challenging part of the operation. In some cases, the key is found on a secondary or tertiary function, with the symbol above the button you need to press rather than on it. In these cases, you need to press the “shift,” “2nd” or “alpha” key to activate the corresponding function for the key. These buttons are often color-coded to make it clear which button you need to press. With this type of calculator, press the button you want to take the factorial of, press the button for the necessary function, then press the factorial button and finally hit “=” for the answer.

Factorials on a Graphing Calculator

On graphing calculators, you may need to do even more to do a factorial. For example, on the TI-84 Plus, you need to enter the math probability menu by pressing “[math]” followed by the left key twice, and finally press “4” to enter the factorial symbol. Check your manual to find the way to complete the operation on a specific graphing calculator.

Entering Factorials Manually

If all else fails, it’s often easy to enter a factorial manually. If the number you want to take the factorial of is small, just enter all of the integers leading up to it with multiplication symbols between each. When you reach the number you’re looking for, hit the “=” button to evaluate the expression.