​ gjyglifilllll

We have that

(-3)^2 + m(-3) + n  = 0

9  - 3m + n  = 0      →     n =   3m - 9       (1)

If x = -3 is the only possible solution...we only have one root...so......the discriminant must  = 0

So

m^2  -  4n  = 0     sub (1)  into this

m^2 - 4 [ 3m - 9 ]  = 0   simplify

m^2 - 12m + 36  =  0       factor

(m - 6)^2  = 0

Which implies that  m  = 6

And n  = 3(6) - 9  = 9

So....our function is   x^2 + 6x + 9 = 0

Check to see that  x = -3  is the only root