Lowest common denominator

The lowest common denominator (also least common denominator and LCD) is the least common multiple of the denominators (bottom parts) of a group of fractions. It makes it easier to add, subtract, and compare fractions.
The LCD of formula_1 and formula_2 is 6. This is because formula_1 and formula_2 equal formula_5 and formula_6. 6 is the smallest number that can be at the bottom of both of those fractions.
The same thing also works with variables: