# FQT Using variables in text and text equations

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## Using variables in the text

It is simple to substitute variables directly in the text. All that is needed is to enclose variables with { }. Each text field has a scope of variables. All variables x of either number or string in the scope of the text can be used to replace the corresponding placeholder {x} in the text.

It is also possible to evaluate an expression directly in the text by adding an equal sign at the beginning of the bracket such as {=x/1000}. It is easier to use if the named variables are not required. However, no error check is done unless the question is being instantiated in the quiz. An example is the rescaling of meters to kilometers below:

What is the speed of the rocket if it travels with distance {=x/1000} km in {t} s?

## Using variables in text equations

Text equations are mathematical expressions or equations that are displayed in the text using math syntax such as:

See Equation Construction and Display for additional information on writing mathematical expressions.

Values of variables can be inserted in text equations in the same way as in the text, that is, by enclosing the variable names with {}. Values of expressions such as {=x/1000} can also be inserted.

Write the following equation in TeX syntax. Upon display, {a}, {b} and {c} will be substituted by the value of these variables:

- {a}
*x*^{2}+ {b}*x*+ {c} = 0

- {a}

\( {a} x^2 + {b} x + {c} = 0 \)

Write the following equation in MathML syntax. Upon display, {a}, {b} and {c} will be substituted by the value of these variables:

- {a}
*x*^{2}+ {b}*x*+ {c} = 0

- {a}

«math xmlns=¨http://www.w3.org/1998/Math/MathML¨» «mn»{a}«/mn» «msup»«mi»x«/mi»«mn»2«/mn»«/msup» «mo»+«/mo» «mn»{b}«/mn» «mi»x«/mi» «mo»+«/mo» «mn»{c}«/mn» «mo»=«/mo» «mn»0«/mn» «/math»

MathML equations are usually created with the aid of an editor. When creating the equation with an editor, it is easier to write a number, say 99, in lieu of the variables, for example:

«math xmlns=¨http://www.w3.org/1998/Math/MathML¨» «mn»99«/mn» «msup»«mi»x«/mi»«mn»2«/mn»«/msup» «mo»+«/mo» «mn»99«/mn» «mi»x«/mi» «mo»+«/mo» «mn»99«/mn» «mo»=«/mo» «mn»0«/mn» «/math»

and then replace the numbers 99 by the variables {a}, {b} and {c} in the HTML code.

Write the following equation in the AsciiMath syntax. Upon display, {a}, {b} and {c} will be substituted by the value of these variables:

- {a}
*x*^{2}+ {b}*x*+ {c} = 0

- {a}

<script src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=AM_HTMLorMML"></script> `{a} x^2 + {b} x + {c} = 0`

Use variables and expressions in text equations that appear in the main question text, the general feedback and the part's feedback of a Formulas question. Use MathML syntax.

*Downloadable question file:* QuadraticEquation.xml

This Formulas question looks like this: