This is made easier IF we can find the real roots right off the bat
So
-3x^3 -6x^2 + 3x + 6 = 0 multiply through by -1
3x^3 + 6x^2 - 3x - 6 = 0 factor
3x^2 ( x - 2) - 3 ( x - 2) = 0
(3x^2 - 3) (x - 2) = 0 so
3x^2 - 3 = 0 x - 2 = 0
3x^2 = 3 x = 2
x^2 = 1
x = ± 1
The roots are -1, 1 , 2
So....if we can perform synthetic division and get alternating signs on the bottom row....then we will have found the lower bound
Test -1 Test - 2 Test - 3
-1 [ 3 6 -3 -6 ] -2 [ 3 6 - 3 - 6 ] - 3 [ 3 6 - 3 - 6 ]
3 -6 -9 9 -18
_____________ ______________ _____________
3 9 NO 3 0 NO 3 -3 6 -24
So x = -3 is the lower bound
Similarly.....if we perfrorm synthetic division and get all postives on the bottom row, then we will have found the upper bound
Test 2
2 [ 3 6 - 3 - 6 ]
6 24 42
_____________
3 12 21 36
So....x = 2 is the upper bound
