is my answer correct? Find the intervals of concavity for the function

Question

Find the intervals of concavity for the function f(x)=2x³+24x²−5x−21

f' (x) = 6x²+48x-5

f" (x) = 12x + 48

12x + 48 = 0

12x + 48 = 0 - 48

12x = -48 divided by 12

x = -4

f" (-8) = -48

f" (-4) = 0

f' (0) = 48

intervals are (my answers)

(-∞, -4) the concave is downwards

(-4, ∞) the concave is upwards

or should i write it like this?

x < -4 concave is downwards

x > -4 concave is upwards

Answer 1

You are correct. You can write it either way