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Solve by (a) Completing the square (b) Using the quadratic formula $$ 2 x^{2}+16 x-24=0 $$

Short Answer

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Question: Solve the quadratic equation $$2x^2 + 16x - 24 = 0$$ using two methods: (a) Completing the square, and (b) Using the quadratic formula. Give the solutions in exact form. Answer: (a) Completing the square: $$x_1 = -4 + \sqrt{28}, \quad x_2 = -4 - \sqrt{28}$$. (b) Using the quadratic formula: $$x_1 = -4 + 2\sqrt{7}, \quad x_2 = -4 - 2\sqrt{7}$$.

Step by step solution

01

(a) Completing the Square

First, look at the equation given: $$2x^2 + 16x - 24 = 0$$. Step 1: Divide the equation by the coefficient of $$x^2$$. $$x^2 + 8x - 12 = 0$$ Step 2: Move the constant term to the other side of the equation. $$x^2 + 8x = 12$$ Step 3: Find the value to complete the square: $$\left(\frac{8}{2}\right)^2 = 4^2 = 16$$ Step 4: Add the value to both sides of the equation. $$x^2 + 8x + 16 = 12 + 16$$ $$x^2 + 8x + 16 = 28$$ Step 5: Rewrite the left side as a perfect square. $$(x + 4)^2 = 28$$ Step 6: Solve for x. $$x + 4 = \pm\sqrt{28} \Rightarrow x = -4 \pm \sqrt{28}$$ So, the solutions are: $$x_1 = -4 + \sqrt{28}, \quad x_2 = -4 - \sqrt{28}$$
02

(b) Using the Quadratic Formula

The quadratic formula is given by: $$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$ Where a, b, and c are coefficients of the quadratic equation $$ax^2 + bx + c = 0$$. Step 1: Identify the coefficients. In the given equation $$2x^2 + 16x - 24 = 0$$, we have: $$a = 2, \quad b = 16, \quad c = -24$$ Step 2: Calculate the discriminant $$\Delta$$. $$\Delta = b^2 - 4ac = 16^2 - 4 \cdot 2 \cdot (-24) = 256 + 192 = 448$$ Step 3: Substitute the coefficients and the discriminant into the quadratic formula and solve for x. $$x = \frac{-16 \pm \sqrt{448}}{4} = \frac{-16 \pm 8\sqrt{7}}{4}$$ So, the solutions are: $$x_1 = -4 + 2\sqrt{7}, \quad x_2 = -4 - 2\sqrt{7}$$ These are the same solutions found in the completing the square method.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Completing the Square
Completing the Square is a method used to solve quadratic equations by transforming a quadratic expression into a perfect square trinomial. Let's walk through it with the example equation: \(2x^2 + 16x - 24 = 0\). The goal is to isolate the variable terms and create a perfect square.
  • First, divide all terms by the coefficient of \(x^2\), which is 2, to simplify the equation to \(x^2 + 8x - 12 = 0\).
  • Move the constant term to the other side, so it looks like \(x^2 + 8x = 12\).
  • To "complete the square," find \(\left(\frac{b}{2}\right)^2\) where \(b\) is the coefficient of \(x\). For \(8x\), this becomes \(4^2 = 16\).
  • Add this square to both sides: \(x^2 + 8x + 16 = 28\). Now, the equation is \( (x + 4)^2 = 28 \).
After completing these steps, we have converted the original equation into \((x + 4)^2 = 28\), which is easier to solve. Simply take the square root of both sides to solve for \(x\), leading to solutions \(x = -4 \pm \sqrt{28}\).
Quadratic Formula
The Quadratic Formula is a universal tool for solving quadratic equations of the form \(ax^2 + bx + c = 0\). The formula is given by \(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\). Let's use this formula to solve the example equation \(2x^2 + 16x - 24 = 0\).
  • Identify the coefficients: \(a = 2\), \(b = 16\), \(c = -24\).
  • Calculate the discriminant \(\Delta = b^2 - 4ac = 448\).
  • Plug these values into the formula: \(x = \frac{-16 \pm \sqrt{448}}{4}\).
By simplifying, this gives us \(x = -4 \pm 2\sqrt{7}\). The Quadratic Formula not only provides the solutions but also offers insight into the nature of the roots (real or complex) based on the discriminant \(\Delta\). Here, \(\Delta > 0\), indicating two distinct real solutions.
Solving Quadratic Equations
Solving Quadratic Equations involves finding the values of \(x\) that satisfy the equation \(ax^2 + bx + c = 0\). Two common methods are Completing the Square and using the Quadratic Formula, as shown in the earlier sections.
  • Completing the Square lets us express the equation as a perfect square, making it easier to manipulate and solve.
  • Quadratic Formula provides a direct, formulaic approach to find the roots when factorization is difficult or impossible.
Each method has its advantages:
- Completing the Square is useful for deriving properties and understanding the geometry of parabolas.
- The Quadratic Formula is a straightforward approach that works universally.
Both methods will yield the same solutions for the same quadratic equation, as demonstrated with \(2x^2 + 16x - 24 = 0\). Mastery of both techniques is valuable for tackling quadratic equations in diverse mathematical contexts.

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