Bradford T. answered 12/13/20
Retired Engineer / Upper level math instructor
We can first simplify this by dividing by 2 and discarding it and then factoring out x.
x(16x3-36x2+27)
Let's just concentrate on the polynomial in the parenthesis using the Rational Root Theorem.
That means we want to look at all rational root of a0/an.
a0 for this polynomial is 27 which has factors ±{1,3,9}.
an for this polynomial is 16 which has factors ±{1,2,4,8,16}
So possible roots are ±{1/1,1/2,1/4,1/8,1/16, 3/2, 3/4, 3/8, 3/16, 9/1,9/2,9/4,9/8,9/16}
Substituting each of for x in 16x3-36x2+27 we find that only 3/2 and -3/4 will produce a value of 0. With a0 being 27, picking the ones with 3 in the numerator first helps speed up the selection.
So we can factor out (2x-3) and (4x+3).
You can use synthetic division to divide out (4x+3).
16 -36 0 27 |-3/4
-12 36 -27
------------------------
16 -48 36 0
16 -48 36 |3/2
24 -36
-----------------
16 -24 0 --> 16x-24 --> x = 24/16 = 3/2 --> (2x-3) again
So the factors are x(2x-3)2(4x+3) or x = 0,3/2, 3/2, -3/4