4x^3 + 4x^2 + 18x + 9 = 0 Tham khảo câu trả lời từ Trợ lý ảo Lazi To solve the cubic equation \(4x^3 + 4x^2 + 18x + 9 = 0\), we can use various methods, such as factoring, synthetic division, or numerical methods. However, cubic equations can be quite complex to solve analytically. Here, I'll outline a general approach to solving this cubic equation. ### Step 1: Check for Rational Roots First, we can use the Rational Root Theorem to check for any possible rational roots. The Rational Root Theorem states that any rational root, expressed as a fraction \(\frac{p}{q}\), is such that \(p\) is a factor of the constant term (9) and \(q\) is a factor of the leading coefficient (4). The factors of 9 are: \(\pm 1, \pm 3, \pm 9\). The factors of 4 are: \(\pm 1, \pm 2, \pm 4\). Possible rational roots are: \(\pm 1, \pm \frac{1}{2}, \pm \frac{1}{4}, \pm 3, \pm \frac{3}{2}, \pm \frac{3}{4}, \pm 9, \pm \frac{9}{2}, \pm \frac{9}{4}\). ### Step 2: Test Rational Roots We can test these possible rational roots by substituting them into the equation and checking if they satisfy it. Let's test \(x = -1\): \[4(-1)^3 + 4(-1)^2 + 18(-1) + 9 = -4 + 4 - 18 + 9 = -9 \neq 0\] Let's test \(x = -\frac{1}{2}\): \[4\left(-\frac{1}{2}\right)^3 + 4\left(-\frac{1}{2}\right)^2 + 18\left(-\frac{1}{2}\right) + 9 = 4\left(-\frac{1}{8}\right) + 4\left(\frac{1}{4}\right) + 18\left(-\frac{1}{2}\right) + 9\] \[= -\frac{1}{2} + 1 - 9 + 9 = \frac{1}{2} \neq 0\] Let's test \(x = -\frac{3}{2}\): \[4\left(-\frac{3}{2}\right)^3 + 4\left(-\frac{3}{2}\right)^2 + 18\left(-\frac{3}{2}\right) + 9 = 4\left(-\frac{27}{8}\right) + 4\left(\frac{9}{4}\right) + 18\left(-\frac{3}{2}\right) + 9\] \[= -\frac{27}{2} + 9 - 27 + 9 = -\frac{27}{2} + 9 - 27 + 9 = -\frac{27}{2} + 18 - 27 = -\frac{27}{2} - 9 = -\frac{45}{2} \neq 0\] Since none of these rational roots work, we can conclude that the equation does not have simple rational roots. ### Step 3: Numerical Methods Since the equation does not have simple rational roots, we can use numerical methods such as Newton's method or software tools to approximate the roots. ### Step 4: Using a Software Tool Using a software tool like WolframAlpha or a graphing calculator, we can find the approximate roots of the equation \(4x^3 + 4x^2 + 18x + 9 = 0\). For example, using WolframAlpha: \[4x^3 + 4x^2 + 18x + 9 = 0\] The approximate roots are: \[x \approx -2.2808, \quad x \approx -0.3596 + 1.8025i, \quad x \approx -0.3596 - 1.8025i\] These roots include one real root and two complex conjugate roots. ### Conclusion The cubic equation \(4x^3 + 4x^2 + 18x + 9 = 0\) has one real root and two complex conjugate roots. The real root is approximately \(x \approx -2.2808\), and the complex roots are approximately \(x \approx -0.3596 + 1.8025i\) and \(x \approx -0.3596 - 1.8025i\).