7. We call fractions with a numerator of 1 and a denominator of a natural number greater than 1 unit fractions. If the unit fraction $\frac{1}{6}$ is expressed as the sum of two different unit fractions, then all possible representations are
7. Let $\frac{1}{6}=\frac{1}{x}+\frac{1}{y}, x<y, x, y \in N$. Then we have $\frac{1}{x}<\frac{1}{6}<\frac{2}{x}$, which means $6<x<12$. When $x=7$, from $\frac{1}{y}=\frac{1}{6}-\frac{1}{7}=\frac{1}{42}$, we get $y=42$; when $x=8$, from $\frac{1}{y}=\frac{1}{6}-\frac{1}{8}=\frac{1}{24}$, we get $y=24$; when $x=9$, from $\frac{1}{y}=\frac{1}{6}-\frac{1}{9}=\frac{1}{18}$, we get $y=18$; when $x=10$, from $\frac{1}{y}=\frac{1}{6}-\frac{1}{10}=\frac{1}{15}$, we get $y=15$; when $x=11$, from $\frac{1}{y}=\frac{1}{6}-\frac{1}{11}=\frac{5}{66}$, we know $y$ is not a natural number.

In summary, the possible representations are $\frac{1}{6}=\frac{1}{7}+\frac{1}{42}=\frac{1}{8}+\frac{1}{24}=\frac{1}{9}+\frac{1}{18}=\frac{1}{10}+\frac{1}{15}$.