First, we'll calculate the roots of the derivative of the
function. These roots are the critical values of the given
function.
y = f(x)
f'(x) =
12x^2 - 12x - 24
We'll put f'(x) =
0
12x^2 - 12x - 24 = 0
We'll
divide by 12:
x^2 - x - 2 =
0
The roots of the first derivative of the function are: x1
= -1 and x2 = 2.
Now, we'll calculate the local extremes of
the function:
f(-1) = 4*(-1) - 6 + 24 +
a
f(-1) = 14 + a
a + 14 =
0
a = -14
f(2) = 32 - 24 - 48
+ a
f(2) = -40 + a
a - 40 =
0
a = 40
We notice that for
values of a in the interval (-14 ; 40), 14 + a > 0 and a - 40 <
0.
According to Rolle's
theorem:
x1 is in the interval (-infinite ;
-1)
x2 is in the interval (-1
; 2)
x3 is in the interval (2
; +infinite)
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