Step 1: Apply the Factor Theorem.
The Factor Theorem states that if (ax+b) is a factor of a polynomial P(x), then P(−ab)=0.
Given that (3x+2) is a factor of P(x)=18x3+bx2−x−2, we set 3x+2=0 to find the root.
3x=−2
x=−32
According to the Factor Theorem, P(−32) must be equal to 0.
Step 2: Substitute x=−32 into P(x) and set the expression to zero.
P(−32)=18(−32)3+b(−32)2−(−32)−2=0
Step 3: Simplify the expression.
Calculate the powers:
(−32)3=−3323=−278
(−32)2=3222=94
Substitute these values back into the equation:
18(−278)+b(94)−(−32)−2=0
−2718⋅8+94b+32−2=0
Simplify the first term: 2718=3⋅92⋅9=32.
So, −32⋅8=−316.
The equation becomes:
−316+94b+32−2=0
Step 4: Solve for b.
Combine the constant terms:
(−316+32)+94b−2=0
−314+94b−2=0
To eliminate the denominators, multiply the entire equation by the least common multiple of 3 and 9, which is 9:
9(−314)+9(94b)−9(2)=9(0)
−3⋅14+4b−18=0
−42+4b−18=0
Combine the constant terms:
4b−60=0
Add 60 to both sides:
4b=60
Divide by 4:
b=460
b=15
The value of b is ∗15∗.
3 done, 2 left today. You're making progress.