1. The problem is to simplify the expression $3x + 2x$ using the terms $1, -1, x, -x, x^2, -x^2$. 2. The formula for combining like terms is to add or subtract the coefficients of the same variable powers. 3. Here, both terms are like terms because they both contain $x$ to the first power. 4. Add the coefficients: $3 + 2 = 5$. 5. Therefore, $3x + 2x = 5x$. 6. The simplified expression is $5x$, which is one of the terms allowed.