/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 18 If \(\log _{3} 81=x-y\) and \(\l... [FREE SOLUTION] | 91Ó°ÊÓ

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If \(\log _{3} 81=x-y\) and \(\log _{2} 32=x+y\) determine the values of \(x\) and \(y\)

Short Answer

Expert verified
The values of \( x \) and \( y \) are \( \frac{9}{2} \) and \( \frac{1}{2} \), respectively.

Step by step solution

01

Convert Logarithmic Equations to Exponential Form

To solve the logarithmic equations, first convert them into exponential form. For \(\log _{3} 81=x-y\): \[ 3^{x-y} = 81 \] Since \ 81 = 3^4 \, we have \[ 3^{x-y} = 3^4 \] Therefore: \ x-y = 4 \
02

Convert the Second Logarithmic Equation to Exponential Form

Next, convert the second given logarithmic equation \( \log _{2} 32=x+y \): \[ 2^{x+y} = 32 \] Since \ 32 = 2^5 \, we have \[ 2^{x+y} = 2^5 \] Therefore: \ x+y = 5 \
03

Form a System of Linear Equations

Using the results from Steps 1 and 2, form a system of linear equations: \[ x - y = 4 \ x + y = 5 \]
04

Solve the System of Linear Equations

Add the two equations to eliminate \( y \): \[ (x - y) + (x + y) = 4 + 5 \] Simplify: \[ 2x = 9 \] Solve for \( x \): \[ x = \frac{9}{2} \]
05

Substitute \( x \) to find \( y \)

Use the value of \( x = \frac{9}{2} \) in one of the original equations. Substitute into \( x + y = 5 \): \[ \frac{9}{2} + y = 5 \] Solve for \( y \): \[ y = 5 - \frac{9}{2} \] \[ y = \frac{10}{2} - \frac{9}{2} \] \[ y = \frac{1}{2} \]

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Key Concepts

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

exponential form
To solve logarithmic equations, one useful method is converting them into their exponential form. This is because exponential equations are often simpler to manage. For instance, take the logarithmic equation \( \log_{3} 81 = x - y \). To convert it to exponential form, recall that the logarithm \( \log_b a = c \) implies \( \ b^c = a \). Thus, \( \log_{3} 81 = x - y \) becomes \( \ 3^{x - y} = 81 \).
Now, since 81 can be written as \( \ 3^4 \), we end up with \( \ 3^{x - y} = 3^4 \). Because the bases are the same (base 3), we can set the exponents equal to each other. Therefore, \( \ x - y = 4 \).
Similarly, for the second equation \( \log_{2} 32 = x + y \), we convert it to exponential form as \( \ 2^{x + y} = 32 \). Since \( \ 32 = 2^5 \), it translates to \( \ 2^{x + y} = 2^5 \). By setting the exponents equal to each other, we get \( \ x + y = 5 \).
Converting to exponential form thus simplifies logarithmic equations substantially, making subsequent steps more straightforward.
system of linear equations
After converting logarithmic equations to exponential form, you often arrive at simpler equations that can form a system of linear equations.
In our example, the converted equations are \( \ x - y = 4 \) and \( \ x + y = 5 \). These two equations together form a system of linear equations.
To solve such a system, you can use various methods:
  • **Substitution Method**: Solve one equation for one variable and substitute that in the other equation.
  • **Elimination Method**: Add or subtract equations to eliminate one variable, then solve for the other.
In this case, the elimination method is quite handy. By adding \( \ x - y \) and \( \ x + y \), the \( \ y \) terms cancel out, simplifying the process.
The added equation is \( \ 2x = 9 \), where solving for \( \ x \) gives \( \ x = \frac{9}{2} \).
To find \( \ y \), substitute \( \ x \) into one of the original equations: \( \ x + y = 5 \) becomes \( \ \frac{9}{2} + y = 5 \). Solving this provides \( \ y = \frac{1}{2} \).
solving logarithms
Solving logarithms involves converting them to forms that are easier to manage, usually exponential form, and employing algebraic methods.
Logarithms are the inverse operations of exponentiation. This means \( \ log_b(a) = c \) is the same as saying \( \ b^c = a \).
When solving logarithmic equations like \( \ log_{3} 81 = x - y \) and \( \ log_{2} 32 = x + y \), follow these steps:
  • **Convert to Exponential Form**: Make the equation linear by converting it so the bases and exponents can be compared directly.
  • **Simplify**: If the numbers are powers of the logarithm's base, simplify by equating exponents.
  • **Form Linear Equations**: Incorporate these simplified forms into linear equations to create a system of equations.
  • **Solve**: Use methods like elimination or substitution to solve the system of equations.
The combined approach of utilizing exponential forms and solving systems of equations allows you to break down complex logarithms into simpler parts. This step-by-step method is efficient and comprehensible when grappling with logarithmic problems.

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Most popular questions from this chapter

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The growth of a new social networking site can be modelled by the exponential function \(N(t)=1.1^{t},\) where \(N\) is the number of users after \(t\) days. a) Write the equation of the inverse. b) How long will it take, to the nearest day, for the number of users to exceed \(1 000 000 ?\)

Solve. Give exact answers. a) \(15=12+\log x\) b) \(\log _{5}(2 x-3)=2\) c) \(4 \log _{3} x=\log _{3} 81\) d) \(2=\log (x-8)\)

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