Subjects algebra

Cubic Roots 77D5A9

Step-by-step solutions with LaTeX - clean, fast, and student-friendly.

Use the AI math solver

1. **State the problem:** We are given that \((2x + 3)\) is a factor of the cubic polynomial \(4x^3 - 12x^2 - 7x + 30\). We need to find all three solutions to the equation \(4x^3 - 12x^2 - 7x + 30 = 0\). 2. **Use the factor to find one root:** Since \(2x + 3 = 0\) is a factor, solve for \(x\): $$2x + 3 = 0 \implies x = -\frac{3}{2}$$ This is one root of the cubic equation. 3. **Divide the cubic polynomial by \(2x + 3\) to find the quadratic factor:** Use polynomial division or synthetic division to divide \(4x^3 - 12x^2 - 7x + 30\) by \(2x + 3\). Set up the division: Divide \(4x^3\) by \(2x\) to get \(2x^2\). Multiply \(2x^2\) by \(2x + 3\): $$2x^2 \times (2x + 3) = 4x^3 + 6x^2$$ Subtract this from the original polynomial: $$\cancel{4x^3} - 12x^2 - 7x + 30 - (\cancel{4x^3} + 6x^2) = -18x^2 - 7x + 30$$ Next, divide \(-18x^2\) by \(2x\) to get \(-9x\). Multiply \(-9x\) by \(2x + 3\): $$-9x \times (2x + 3) = -18x^2 - 27x$$ Subtract: $$-18x^2 - 7x + 30 - (-18x^2 - 27x) = 20x + 30$$ Divide \(20x\) by \(2x\) to get \(10\). Multiply \(10\) by \(2x + 3\): $$10 \times (2x + 3) = 20x + 30$$ Subtract: $$20x + 30 - (20x + 30) = 0$$ So the quotient is \(2x^2 - 9x + 10\). 4. **Solve the quadratic equation:** $$2x^2 - 9x + 10 = 0$$ Use the quadratic formula: $$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$ where \(a=2\), \(b=-9\), \(c=10\). Calculate the discriminant: $$\Delta = (-9)^2 - 4 \times 2 \times 10 = 81 - 80 = 1$$ Calculate the roots: $$x = \frac{9 \pm \sqrt{1}}{2 \times 2} = \frac{9 \pm 1}{4}$$ So, $$x_1 = \frac{9 + 1}{4} = \frac{10}{4} = \frac{5}{2}$$ $$x_2 = \frac{9 - 1}{4} = \frac{8}{4} = 2$$ 5. **Final solutions:** The three solutions to \(4x^3 - 12x^2 - 7x + 30 = 0\) are: $$x = -\frac{3}{2}, \quad x = 2, \quad x = \frac{5}{2}$$