1. We are asked to factor the cubic polynomial $2x^3 + 9x^2 - 6x - 5$.
2. First, try to find rational roots using the Rational Root Theorem. Possible roots are factors of the constant term $-5$ divided by factors of the leading coefficient $2$: $\pm1, \pm\frac{1}{2}, \pm5, \pm\frac{5}{2}$.
3. Test $x=\frac{1}{2}$:
$$2\left(\frac{1}{2}\right)^3 + 9\left(\frac{1}{2}\right)^2 - 6\left(\frac{1}{2}\right) - 5 = 2\cdot\frac{1}{8} + 9\cdot\frac{1}{4} - 3 - 5 = \frac{1}{4} + \frac{9}{4} - 8 = \frac{10}{4} - 8 = 2.5 - 8 = -5.5 \neq 0$$
4. Test $x=-1$:
$$2(-1)^3 + 9(-1)^2 - 6(-1) - 5 = -2 + 9 + 6 - 5 = 8 \neq 0$$
5. Test $x=1$:
$$2(1)^3 + 9(1)^2 - 6(1) - 5 = 2 + 9 - 6 - 5 = 0$$
So, $x=1$ is a root.
6. Use polynomial division or synthetic division to divide $2x^3 + 9x^2 - 6x - 5$ by $(x - 1)$:
Synthetic division:
Coefficients: 2 | 9 | -6 | -5
Bring down 2.
Multiply 2 by 1: 2, add to 9: 11.
Multiply 11 by 1: 11, add to -6: 5.
Multiply 5 by 1: 5, add to -5: 0 (remainder).
So quotient is $2x^2 + 11x + 5$.
7. Factor the quadratic $2x^2 + 11x + 5$:
Find two numbers that multiply to $2 \times 5 = 10$ and add to $11$: these are $10$ and $1$.
Rewrite:
$$2x^2 + 10x + x + 5 = 2x(x + 5) + 1(x + 5) = (2x + 1)(x + 5)$$
8. Therefore, the full factorization is:
$$\boxed{(x - 1)(2x + 1)(x + 5)}$$
Factor Cubic
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