Equation field guide
Multiplication: combining factors
Multiplication scales one quantity by another. A dot, a cross, or adjacent symbols can indicate a product.
Find the factors
In 2x, the number 2 is a coefficient and x is multiplied by it. In ab, a and b are multiplied when they are separate variables; a multi-letter name such as “rate” is different and should be identified by the article.
Parentheses group factors: a(b + c) means multiply a by the whole sum b + c. Read what lies inside the parentheses first.
Units provide a check
If speed has units metres per second and time has units seconds, speed × time has units metres. If power has units joules per second, power × time has units joules of energy.
A correct unit relationship cannot identify an unknown symbol by itself, but it can rule out an incompatible interpretation.
Changing one factor
If the other factor stays fixed, doubling one factor doubles the product. This does not imply that the factor can vary independently in the real system; dependencies and bounds come from the model.