2n^2-8n=9
divide by 2
2(n^2-4n) =9
add (4/2)^2 =4 to each side completing the square
(n^2-4n+4 ) =9/2+4
(n-2)^2 = 9/2+8/2
(n-2)^2 =17/2
take the square root of each side
n-2 = +-sqrt(17/2)
add 2 to each side
n = 2+- sqrt (17/2)
Answer:2+ sqrt (17/2),2- sqrt (17/2)