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Explain the mistake that is made. $$\begin{aligned}2 x^{2}-4 x &=3 \\\2\left(x^{2}-2 x\right) &=3 \\\2\left(x^{2}-2 x+1\right) &=3+1 \\\2(x-1)^{2} &=4 \\\\(x-1)^{2} &=2 \\\x-1 &=\pm \sqrt{2} \\\x &=1 \pm \sqrt{2} \end{aligned}$$

Short Answer

Expert verified
The mistake is in completing the square with incorrect adjustment on the right side.

Step by step solution

01

Identify the Initial Equation

The initial equation provided is \(2x^2 - 4x = 3\). The problem involves solving this quadratic equation by completing the square.
02

Factoring Out a 2

The next step involves factoring out a \(2\) from the left side of the equation: \(2(x^2 - 2x) = 3\). This step aims to simplify the expression inside the parentheses.
03

Completing the Square Incorrectly

The next transformation describes an incorrect attempt at completing the square: \(2(x^2 - 2x + 1) = 3 + 1\). The error lies in the assumption that adding \(1\) inside the parentheses only impacts the right side by \(+1\). In reality, because of the \(2\) factor outside the parentheses, it should have been \(2 \times 1 = 2\), affecting the right side as \(2\), making it \(3 + 2\), not \(3 + 1\).
04

Correct Process of Completing the Square

The correct approach should have been: \(2(x^2 - 2x + 1) = 3 + 2\), simplifying to \(2(x-1)^2 = 5\), not \(2(x-1)^2 = 4\) as computed incorrectly. Thus, \((x-1)^2 = \frac{5}{2}\).
05

Solve for \(x\)

From \((x-1)^2 = \frac{5}{2}\), take the square root of both sides: \(x - 1 = \pm \sqrt{\frac{5}{2}}\). This simplifies to \(x = 1 \pm \sqrt{\frac{5}{2}}\).

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Key Concepts

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

Quadratic Equation
Quadratic equations are foundational in algebra. They take the standard form \( ax^2 + bx + c = 0 \). In our given exercise, the equation is \( 2x^2 - 4x = 3 \). While this may not be in the standard form, it can easily be rearranged to make sense as a quadratic. By subtracting 3 from both sides, it becomes \( 2x^2 - 4x - 3 = 0 \).
This shows its quadratic nature with, \( a = 2 \), \( b = -4 \), and \( c = -3 \). Quadratic equations can be solved by multiple methods, such as factoring, completing the square, and using the quadratic formula. Recognizing a quadratic equation is crucial before choosing the best method to solve it. Simplifying it to the right format allows the application of various solutions like in the given exercise, where we initially complete the square.
Factoring
Factoring is a handy approach to solve quadratic equations, particularly when they can be easily expressed as a product of binomials. In the exercise, factoring played an early role, when both terms in the left were divided by 2 to simplify the equation's left side: \( 2(x^2 - 2x) = 3 \). Factoring out terms when appropriate helps reduce complexity, making it easier to apply the correct solving technique, whether proceeding with completing the square or otherwise.
The key to factoring is identifying terms or factors that simplify the equation. This can be especially useful when the resulting expression can be further manipulated, such as in efforts to complete the square later in the exercise. Observing patterns and using common factor techniques allows you to convert complex expressions into more manageable forms. Furthermore, factoring is often the preferred method when the roots of the quadratic are rational and easily recognizable.
Square Root Method
The square root method is particularly useful in equations that have either been completed to a perfect square or are naturally perfect squares. In the exercise, after correctly applying the completing the square process, the equation \((x-1)^2 = \frac{5}{2}\) emerged.
To solve this equation, the square root method comes into play. By taking the square root of both sides, we find \( x - 1 = \pm \sqrt{\frac{5}{2}} \). This operation leaves us with two potential answers for \( x \), emphasizing the fundamental principle that squaring both positive and negative numbers result in the same value.
  • Always remember, taking the square root introduces both a positive and negative solution: \( \sqrt{\frac{5}{2}} \text{ and } -\sqrt{\frac{5}{2}} \).
  • Rearrange the equation to isolate the variable, resulting in: \( x = 1 \pm \sqrt{\frac{5}{2}} \).
Applying this method is crucial for accurately solving quadratic equations after the completion of the square process, avoiding the pitfalls of incorrect adjustments in equals as seen in the initial mistake from the original attempt.

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Most popular questions from this chapter

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