I cant see where im going wrong here can somebody point it out to me please. Il show my workings.

Trying to find the x-intercept

y= -2(x-3)^2 +8

so when y=o

0= -2(x+3)^2 +8

8= -2(x+3)^2

-4= (x+3)^2

-4= x^2 + 6x +9

x^2 + 6x + 13 now i dont know whats going on, if i use the formula -b +- (square root) b^2 -4ac /2a i get square root -16 which means x is not a real number? i think im going wrong somewhere on top.

any help appreciated my math is rusty