Math Problem Statement

lg(x) + lg(x+3) = 1

Solution

The equation provided in the image is:

log(x)+log(x+3)=1\log(x) + \log(x+3) = 1

To solve this equation, let's apply the properties of logarithms.

Step 1: Combine the logarithmic terms using the product rule for logarithms:

log(x)+log(x+3)=log(x(x+3))=log(x2+3x)\log(x) + \log(x + 3) = \log(x(x + 3)) = \log(x^2 + 3x)

Now the equation becomes: log(x2+3x)=1\log(x^2 + 3x) = 1

Step 2: Convert the logarithmic equation to its exponential form:

x2+3x=101=10x^2 + 3x = 10^1 = 10

Step 3: Solve the quadratic equation:

x2+3x10=0x^2 + 3x - 10 = 0

We can solve this using the quadratic formula:

x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

Here, a=1a = 1, b=3b = 3, and c=10c = -10. Substituting these values into the quadratic formula:

x=3±324(1)(10)2(1)x = \frac{-3 \pm \sqrt{3^2 - 4(1)(-10)}}{2(1)} x=3±9+402x = \frac{-3 \pm \sqrt{9 + 40}}{2} x=3±492x = \frac{-3 \pm \sqrt{49}}{2} x=3±72x = \frac{-3 \pm 7}{2}

So, the two possible solutions are:

x=3+72=2x = \frac{-3 + 7}{2} = 2 x=372=5x = \frac{-3 - 7}{2} = -5

Step 4: Verify the solutions:

  • For x=2x = 2, both log(2)\log(2) and log(2+3)\log(2 + 3) are defined, so x=2x = 2 is a valid solution.
  • For x=5x = -5, log(5)\log(-5) is undefined because the logarithm of a negative number does not exist in the set of real numbers. So, x=5x = -5 is not a valid solution.

Final Solution:

The only valid solution is: x=2x = 2

Would you like more details or have any questions about this process?

Here are 5 related questions to expand your understanding:

  1. How does the product rule of logarithms work, and why is it applicable here?
  2. What are the steps to convert a logarithmic equation to an exponential one?
  3. Could the quadratic formula always be used to solve any quadratic equation?
  4. Why is the logarithm of a negative number undefined?
  5. Can logarithmic equations have multiple solutions, and how do you check their validity?

Tip: Always check the domain of logarithmic functions to ensure that solutions are valid—logarithms are only defined for positive arguments.

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Math Problem Analysis

Mathematical Concepts

Logarithms
Quadratic Equations

Formulas

Product rule of logarithms: lg(a) + lg(b) = lg(ab)
Quadratic equation formula: ax^2 + bx + c = 0
Logarithmic to exponential form: log_b(a) = c -> a = b^c

Theorems

Quadratic Formula
Properties of Logarithms

Suitable Grade Level

Grades 9-12