Quadratics

If x = -3, then (x+3)(x+3) is equal to $x^2+mx+n$ . (x+3)(x+3) is equal to $x^2+6x+9$ , making m equal to $\boxed{6}$ . $\square$

The quadratic equation can have 2 real roots, 1 equal root (it can be real or imaginary), and 2 imaginary roots.

The quadratic equation that $x ^ { 2 } + mx + n = 0$ has an equal root that $x = - 3$ , then we get $x + 3 = 0$ .

Let's square it.

Then $( x + 3 ) ^ { 2 } = 0$ .

So $x ^ { 2 } + 6x + 9 = 0$ .

Final, the value of $m$ is $x ^ { 2 } + mx + n = 0$ equals $\boxed { 6 }$ , and $n$ is $\boxed { 9 }$ .

So the answer is $m = 6, n = 9$ , but the question is asking the value of $m$ , so the answer is $\boxed { 6 }$ .