If f(x)= 2x^3-x^2+3x+10 and g(x)= x^3+3x^2+2x+4, determine
when f(x)>g(x) using a factor table strategy.
I don't know about "factor table strategy", but
here is the way I'd go about solving the problem:
Get 0 on the right:
We find the critical values, which are the zeros of
Use synthetic division, trying the factors of 6, which are ±1,±2,±3,±6
1 | 1 -4 1 6
| 1 -3 -2
1 -3 -2 4
Remainder isn't 0. Try -1
-1 | 1 -4 1 6
| -1 5 -6
1 -5 6 0
So factors as
(x+1)(x2-5x+6)
and it factors completely as
(x+1)(x-2)(x-3) > 0
So the critical numbers are -1,2, and 3
Intervals to test (between and beyond those):
1.
Test x=-2, (-2+1)(-2-2)(-2-3) > 0
(-1)(-4)(-5) > 0
-20 > 0
FALSE!
2.
Test 0, (0+1)(0-2)(0-3) > 0
(1)(-2)(-3) > 0
6 > 0
TRUE!
3.
Test 2.5, (2.5+1)(2.5-2)(2.5-3) > 0
(3.5)(0.5)(-0.5) > 0
-0.875 > 0
FALSE!
Test 4, (4+1)(4-2)(4-3) > 0
(5)(2)(1) > 0
10 > 0
TRUE!
So f(x) > g(x) when -1 < x < 2, and when x > 3
Edwin