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 $\frac{1}{2}$ and $\frac{2}{3}$ is 6. This is because $\frac{1}{2}$ and $\frac{2}{3}$ equal $\frac{3}{6}$ and $\frac{4}{6}$. 6 is the smallest number that can be at the bottom of both of those fractions.

The same thing also works with variables:

$\frac{1}{2x}+\frac{3}{x^2}=\frac{1}{2x}\cdot \frac{x}{x}+\frac{3}{x^2}\cdot \frac{2}{2}=\frac{x}{2x^2}+\frac{6}{2x^2}=\frac{x+6}{2x^2}$