### Instruction: Completely factor the following expression: $9x^2+3x$.### Response: To factor a polynomial, I want to look for common factors in each term that I can pull out of the expression.
In this case, I see that both terms are divisible by 3, so I can start by factoring out 3 from the expression: $9x^2+3x = 3(3x^2+x)$.
Now, I have a simpler polynomial inside the parentheses that I want to factor further.
I notice that both terms are multiples of x, so I can also factor out x from the expression: $3x^2+x = x(3x+1)$.