the second derivative of (sqrt((2x^3)+(6x)+(8)))

y = sqrt(2x^3 + 6x + 8)

= (2x^3 + 6x + 8)^(1/2)

y' = 1/2 (2x^3 + 6x + 8)^(-1/2) * (6x + 6)
= (3x+3)/(2x^3 + 6x + 8)^(1/2)