Why Are My Logarithmic Equation Solutions Extraneous?

  • MHB
  • Thread starter cbarker1
  • Start date
  • Tags
    Logarithmic
So, the solutions are x=-1, x=6That's all.In summary, the conversation is about solving for x in a logarithmic equation, where the solution in the book is -1, but the individual who provided the solution realized that there was a mistake in the factorization, and the correct solutions are actually x=-1 and x=6.
  • #1
cbarker1
Gold Member
MHB
349
23
Solve for x

$\log\left({2-x}\right)+\log\left({3-x}\right)=\log\left({12}\right)$
$\log\left({(2-x)(3-x})\right)=\log\left({12}\right)$
$\left(2-x)\right)\left(3-x)\right)=12$
${x}^{2}-5x-6=0$
$\left(x-2)\right)\left(x-3)\right)=0$
$x=2, x=3$

I have a problem with solutions because both is extraneous.

$\log\left({2-2}\right)+\log\left({3-2}\right)=\log\left({12}\right)$
$\log\left({0}\right)+\log\left({1}\right)=\log\left({12}\right)$
This solution is extraneous as well as the other solution.

The solution in the back of the book is -1.

Where did I made a mistake?Thank you
 
Mathematics news on Phys.org
  • #2
Cbarker1 said:
Solve for x

$\log\left({2-x}\right)+\log\left({3-x}\right)=\log\left({12}\right)$
$\log\left({(2-x)(3-x})\right)=\log\left({12}\right)$
$\left(2-x)\right)\left(3-x)\right)=12$
${x}^{2}-5x-6=0$
$\color{red}(x-2)(x-3)=0$
$x=2, x=3$

...

Hello,

I've marked the line where you made a tiny (but fatal) mistake.

After facvtorization you should come out with

\(\displaystyle x^2-5x-6 = (x+1)(x-6)=0\)
 

FAQ: Why Are My Logarithmic Equation Solutions Extraneous?

What is a logarithmic equation?

A logarithmic equation is an equation that contains at least one logarithmic term. Logarithmic functions are the inverse of exponential functions and are used to solve for the power or exponent in an exponential expression.

How do you solve a logarithmic equation?

To solve a logarithmic equation, you must use the properties of logarithms to isolate the logarithmic term. This involves using the power rule, product rule, and quotient rule. Once the logarithmic term is isolated, you can solve for the variable using algebraic methods.

What are the properties of logarithms?

The main properties of logarithms are the power rule, product rule, and quotient rule. The power rule states that logb(xm) = mlogb(x). The product rule states that logb(xy) = logb(x) + logb(y). The quotient rule states that logb(x/y) = logb(x) - logb(y). These rules can be used to simplify logarithmic expressions and solve logarithmic equations.

What are some real-world applications of logarithmic equations?

Logarithmic equations are used in a variety of fields, including finance, science, and engineering. In finance, they are used to calculate compound interest and growth rates. In science, they are used to measure the intensity of earthquakes and sound waves. In engineering, they are used to model the decay of radioactive materials and the flow of electricity in circuits.

What is the difference between a logarithmic equation and an exponential equation?

A logarithmic equation and an exponential equation are inverses of each other. In an exponential equation, the variable is in the exponent, while in a logarithmic equation, the variable is in the base. For example, the exponential equation 2x = 8 can be rewritten as log2(8) = x. In general, exponential equations are used to represent growth or decay, while logarithmic equations are used to solve for the exponent or power in an exponential expression.

Similar threads

Replies
13
Views
2K
Replies
6
Views
2K
Replies
2
Views
3K
Replies
3
Views
1K
Replies
3
Views
2K
Replies
1
Views
1K
Back
Top