formula rearrangement

A formula is written to give you one particular quantity, but life does not always hand you the convenient pieces. Formula rearrangement is the act of re-aiming the formula: starting from one that gives, say, area, and rewriting it so it hands you a side length instead.

Mechanically it is just solving a literal equation. You pick the variable you now want alone, then peel away everything around it with inverse operations applied to both sides, treating all other symbols as constants.

The payoff is reuse: one well-rearranged formula lets you compute the new target directly, without re-solving from scratch every time. Just keep track of any restriction, such as a divisor that must not be zero.