Solve by taking the square too of both sides.
3(c+3)^2-81=0

x = -3 ±3sqrt(3)

Step-by-step explanation:

3(x+3)^2-81=0

Add 81 to each side

3(x+3)^2=81

Divide each side by 3

3/3(x+3)^2=81/3

(x+3)^2=27

Take the square root of each side

sqrt ((x+3)^2)=±sqrt(27)

x+3 =±sqrt(9*3)

x+3 =±sqrt(9)*sqrt(3)

x+3 =±3sqrt(3)

Subtract 3 from each side

x = -3 ±3sqrt(3)