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FACTORIZE \( 4 x^{2}-20 x-9 \)

Ask by Mejia Vargas. in South Africa
Mar 18,2025

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Tutor-Verified Answer

Answer

The expression \( 4x^{2} - 20x - 9 \) can be factored as \( 4\left(x - \frac{5 - \sqrt{34}}{2}\right)\left(x - \frac{5 + \sqrt{34}}{2}\right) \).

Solution

Solve the quadratic equation by following steps: - step0: Solve using the quadratic formula: \(4x^{2}-20x-9=0\) - step1: Solve using the quadratic formula: \(x=\frac{20\pm \sqrt{\left(-20\right)^{2}-4\times 4\left(-9\right)}}{2\times 4}\) - step2: Simplify the expression: \(x=\frac{20\pm \sqrt{\left(-20\right)^{2}-4\times 4\left(-9\right)}}{8}\) - step3: Simplify the expression: \(x=\frac{20\pm \sqrt{544}}{8}\) - step4: Simplify the expression: \(x=\frac{20\pm 4\sqrt{34}}{8}\) - step5: Separate into possible cases: \(\begin{align}&x=\frac{20+4\sqrt{34}}{8}\\&x=\frac{20-4\sqrt{34}}{8}\end{align}\) - step6: Simplify the expression: \(\begin{align}&x=\frac{5+\sqrt{34}}{2}\\&x=\frac{20-4\sqrt{34}}{8}\end{align}\) - step7: Simplify the expression: \(\begin{align}&x=\frac{5+\sqrt{34}}{2}\\&x=\frac{5-\sqrt{34}}{2}\end{align}\) - step8: Rewrite: \(x_{1}=\frac{5-\sqrt{34}}{2},x_{2}=\frac{5+\sqrt{34}}{2}\) To factor the expression \( 4x^{2} - 20x - 9 \), we first need to find its roots by solving the equation \( 4x^{2} - 20x - 9 = 0 \). ### Step 1: Solve the Quadratic Equation Using the quadratic formula, we find the roots: \[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \] Here, \( a = 4 \), \( b = -20 \), and \( c = -9 \). Calculating the discriminant: \[ b^2 - 4ac = (-20)^2 - 4 \cdot 4 \cdot (-9) = 400 + 144 = 544 \] Now, substituting into the quadratic formula: \[ x = \frac{20 \pm \sqrt{544}}{8} \] ### Step 2: Simplify the Roots The square root of 544 can be simplified: \[ \sqrt{544} = \sqrt{16 \cdot 34} = 4\sqrt{34} \] Thus, the roots are: \[ x_{1} = \frac{20 - 4\sqrt{34}}{8} = \frac{5 - \sqrt{34}}{2} \] \[ x_{2} = \frac{20 + 4\sqrt{34}}{8} = \frac{5 + \sqrt{34}}{2} \] ### Step 3: Write the Factored Form Using the roots, we can express the quadratic in its factored form: \[ 4x^{2} - 20x - 9 = 4\left(x - \frac{5 - \sqrt{34}}{2}\right)\left(x - \frac{5 + \sqrt{34}}{2}\right) \] ### Final Factored Form Thus, the factored form of \( 4x^{2} - 20x - 9 \) is: \[ 4\left(x - \frac{5 - \sqrt{34}}{2}\right)\left(x - \frac{5 + \sqrt{34}}{2}\right) \]

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The Deep Dive

To factor the quadratic \( 4x^{2} - 20x - 9 \), we can use the method of factoring by grouping or the quadratic formula. First, let’s find two numbers that multiply to \( (4)(-9) = -36 \) and add up to \( -20 \). These two numbers are \( -18 \) and \( 2 \). Thus, we rewrite the equation: \( 4x^{2} - 18x + 2x - 9 \). Now, we can group: \( (4x^{2} - 18x) + (2x - 9) \) Factoring out common terms gives us: \( 2x(2x - 9) + 1(2x - 9) = (2x - 9)(2x + 1) \). So, the factored form is: \( (2x - 9)(2x + 1) \). To verify, you can expand \( (2x - 9)(2x + 1) \) to check if it gives the original expression. Give it a try! There you have it! Happy factoring! 🎉

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