Quadratic formula
Dimensional analysis

If the constants a {\displaystyle a}, b {\displaystyle b}, and/or c {\displaystyle c} are not unitless then the quantities x {\displaystyle x} and b a {\displaystyle {\tfrac {b}{a}}} must have the same units, because the terms a x 2 {\displaystyle \textstyle ax^{2}} and b x {\displaystyle bx} agree on their units. By the same logic, the coefficient c {\displaystyle c} must have the same units as b 2 a {\displaystyle {\tfrac {b^{2}}{a}}}, irrespective of the units of x {\displaystyle x}. This can be a powerful tool for verifying that a quadratic expression of physical quantities has been set up correctly.
combination:repeat_prompt, oulipo:avoid_letter[t]