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Solve the logarithmic equation algebraically. Approximate the result to three decimal places.\(\log _{10} 4 x-\log _{10}(12+\sqrt{x})=2\)

Short Answer

Expert verified
The unique solution to the given logarithmic equation is \(x = 121.637\) after verifying that it does not result to a negative number within the logarithm and thus, it is not an extraneous solution.

Step by step solution

01

Use the properties of logarithms

The log difference can be turned into a quotient by using the properties of logarithms. The equation can be rewritten as \( \log _{10} (4x/(12+ \sqrt{x})) = 2 \)
02

Remove the logarithm from the equation

Using equivalent exponential form, \(4x/(12+ \sqrt{x}) equals to 10^2 or 100. Hence the equation becomes: \(4x=100 * (12 + \sqrt{x})\)
03

Get rid of the denominator

Multiply all terms by the denominator to remove fractions: \( 4x=100*12 + 100*\sqrt{x} \) which simplifies to \( 4x=1200+100*\sqrt{x} \)
04

Isolate terms involving square roots

Rearrange the equation to isolate the term with the square root: \(100 * \sqrt{x} = 4x - 1200 \)
05

Square both sides

Eliminate the square root by squaring both sides of the equation: \( (100*\sqrt{x})^2 = (4x-1200)^2 \)
06

Solve for x

The obtained quadratic equation is solved to get the value of x. Due consideration is given to possible extraneous roots which may not satisfy the original equation.

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Key Concepts

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

Properties of Logarithms
Logarithms have unique characteristics that allow for the simplification and solving of equations that involve exponential expressions. A key property used in solving logarithmic equations is the ability to convert the difference of two logarithms into the logarithm of a quotient. This is formally known as the Quotient Rule, which states that \(\log_b a - \log_b c = \log_b(\frac{a}{c})\).

In the exercise provided, this property is used in the first step to combine two separate logarithmic terms involving \(4x\) and \(12 + \sqrt{x}\) into a single logarithm. Understanding this rule helps students see the relationship between the terms within the logarithm and to subsequently transition from logarithmic to exponential form smoothly.
Exponential Form
The exponential form is the inverse of the logarithmic form and is essential in solving logarithmic equations. Given the logarithmic equation \(\log_b x = y\), the equivalent exponential form is \(b^y = x\). This transformation is necessary because it frees the variable from the confines of the logarithm and allows further algebraic manipulation.

During the second step of the exercise, \(\log_{10}(4x/(12+ \sqrt{x})) = 2\) is translated to its exponential counterpart, \(100 = 4x/(12 + \sqrt{x})\), thus setting the stage to isolate the variable and solve the equation. One must be cautious with the exponential form as it can sometimes introduce extraneous solutions, which are apparent solutions that don't actually satisfy the original equation.
Square Root Isolation
Square root isolation is the process of manipulating an equation to have a square root term by itself on one side of the equation. This is a crucial step when solving equations where the variable is under a square root, because once isolated, we can square both sides of the equation to eliminate the square root and continue solving the equation in a more straightforward algebraic way.

In the given problem's fourth step, the square root containing the variable \(x\) is isolated on one side resulting in \(100 * \sqrt{x} = 4x - 1200\). Isolating the square root is a strategic move that simplifies the process of solving the rest of the equation as seen in subsequent steps.
Quadratic Equations
Quadratic equations are second-degree polynomial equations in the form \(ax^2 + bx + c = 0\). They are a fundamental part of algebra and can be solved through various methods including factoring, completing the square, using the quadratic formula, or graphing. Solving quadratics becomes necessary after isolating and squaring a square root that contains the variable.

In the solution under consideration, after squaring the isolated square root, a quadratic equation in standard form is obtained and can be solved to find the value(s) of \(x\). It's important to remember that squaring both sides of the equation can introduce extraneous solutions, thus any solution found must be checked against the original equation to make sure it's valid. This example illustrates well how different algebraic concepts link together to solve an equation.

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Most popular questions from this chapter

Find the constants \(C\) and \(k\) such that the exponential function \(y=C e^{k t}\) passes through the points on the graph.Learning Curve The management at a factory has found that the maximum number of units a worker can produce in a day is 40 . The learning curve for the number of units \(N\) produced per day after a new employee has worked \(t\) days is given by \(N=40\left(1-e^{k t}\right)\) After 20 days on the job, a particular worker produced 25 units in 1 day. (a) Find the learning curve for this worker (first find the value of \(k\) ). (b) How many days should pass before this worker is producing 35 units per day?

Find the time required for a \(\$ 1000\) investment to double at interest rate \(r\), compounded continuously.\(r=0.0625\)

Solve the logarithmic equation algebraically. Approximate the result to three decimal places.\(7+3 \ln x=5\)

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Solve for \(y\) in terms of \(x\).\(\ln y=2 \ln x+\ln (x-3)\)

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