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# Choosing the letter

In an algebraic expression, the choice of the letter is not important.

However some letters are used more frequently depending on their interpretation in the formula.

Letter Range Meaning Values Expression
$x$, $y$, $z$ $\R$ Position, generic variable $-3.14$ $\Tred{x}+\Torange{y}-3$
$t$, $s$ $\R$ Time $1.1$ $\Tred{t}^2$, $3\Torange{s}$
$m$, $n$, $p$, $q$ $\Z^+$, $\Z$ Index, generic integer $12$ $\Tred{n} = \Torange{p}^2 + \Tgreen{q}$
$\theta$ $\R$ Angle $45^\circ$ $\cos(\Tred{\theta})$