Expand and simplify (3a+b)(a-2b).

To expand, you would multiply each term in the first bracket set by each term of the second bracket set. Thus, your expansion would mean:3a^2 -6ab + ab -2b^2
To simplify, note that there are two 'ab' terms in this equation. Add them together. The final, expanded and simplified answer would be:3a^2 -5ab - 2b^2