For assignments in the body of the course and for the calculator tool, you enter plain text, and the edX system then converts your text into numbers and symbols that appear below the response field.

Both the calculator and the response fields in math problems accept a selection of characters that represent numbers, operators, constants, functions, and other mathematical concepts. You might recognize parts of this system if you have used math programs before.

If your course offers the calculator tool, the calculator appears as a small icon on all pages in the body of the course. To open the calculator, select the calculator icon. To close the calculator, select the X that appears when the calculator is open.

The calculator includes an information page that shows an abbreviated version of the information in this topic. To see the information page, select the circled `i`

icon next to the input field.

## Plain Text Guidelines

When you enter your plain text into the calculator or the response field, follow these guidelines.

**Arithmetical operations**: Use standard characters for addition (+), subtraction (-), multiplication (*), and division (/).**Multiplication**: Be sure to indicate multiplication explicitly. That is, instead of`mc^2`

type`m*c^2`

, and instead of`5a+4b+3c`

type`5*a+4*b+3*c`

.

**Operation order**: Use parentheses (`( )`

) to specify the order of operations and to make your expression as clear as possible. Use curved parentheses (`( )`

) only. Do not use brackets (`[ ]`

) or braces (`{ }`

).**Exponents or superscripts**: Insert a caret (^) before an exponent or superscript. If the exponent or superscript includes multiple characters or is an expression, surround the expression with parentheses. For example, you can enter`x^n`

or`x^(n-1)`

.**Subscripts**: Insert an underscore (_) before a subscript to indicate a subscript. If the subscript has multiple characters, type the characters without a space. For example, you can enter`v_IN-v_OUT`

. Note, however, that subscripts cannot currently include operators or parentheses.- Avoid whitespace.
- Do not use equal signs (=).
- Because the system is case-sensitive, make sure you use uppercase and lowercase letters carefully.

**Note**: The edX system accepts both constants and metric affixes. Be careful to distinguish between constants and metric affixes. Constants stand alone, while metric affixes must be combined with numbers. For example, `c`

can be a constant representing the speed of light or a metric affix meaning “centi”. When you use `c`

as a metric affix, do not include a space between `c`

and the number. When you use `c`

as a constant, indicate multiplication explicitly. The following examples show the difference:

`2c`

=`0.02`

(2 multiplied by 0.01)`2*c`

=`599584916.0`

(the speed of light multiplied by 2)`2M`

=`2,000,000`

(2 multiplied by 1,000,000)`2*M`

= 2 multiplied by the variable M

For more information, see Scientific Notation and Metric Affixes or Constants.