Simplifying expressions or equations is frequently a key step in solving problems in algebra. To simplify a collection of terms, only those of the same type can be combined. Numbers can be combined with numbers. Terms in $$x$$ can be added to or subtracted from terms in $$x$$ e.g. $$5x - 2x$$ is $$3x$$. Terms in $$x^2$$ are different again and must be treated separately. When combining terms, it is essential to take note of the sign in front of each term.