46. (9th grade) Find the sum

$$
\frac{1}{2 \cdot 5}+\frac{1}{5 \cdot 8}+\frac{1}{8 \cdot 11}+\ldots+\frac{1}{(3 n-1)(3 n+2)}
$$
46. Let's represent each term in the following form: $\frac{1}{(3 n-1)(3 n+2)}=$ $=\frac{1}{3}\left(\frac{1}{3 n-1}-\frac{1}{3 n+2}\right)$. Then, the desired sum, after combining like terms, will have the form: $S=\frac{1}{3}\left(\frac{1}{2}-\frac{1}{3 n+2}\right)$. Answer: $S=\frac{n}{2(3 n+2)}$.