Math Problem Statement

2log3x – log3(x + 4) = 2

solve for x

Solution

We are given the equation:

2log3xlog3(x+4)=22 \log_3{x} - \log_3{(x+4)} = 2

Step 1: Apply the properties of logarithms

We can use the power rule of logarithms to simplify the first term:

2log3x=log3x22 \log_3{x} = \log_3{x^2}

Thus, the equation becomes:

log3x2log3(x+4)=2\log_3{x^2} - \log_3{(x+4)} = 2

Step 2: Apply the quotient rule of logarithms

The quotient rule of logarithms states that:

logbAlogbB=logb(AB)\log_b{A} - \log_b{B} = \log_b{\left(\frac{A}{B}\right)}

Applying this to the equation, we get:

log3(x2x+4)=2\log_3\left(\frac{x^2}{x+4}\right) = 2

Step 3: Convert the logarithmic equation to an exponential form

Using the definition of logarithms, logbA=C\log_b{A} = C implies A=bCA = b^C, we convert the equation to:

x2x+4=32\frac{x^2}{x+4} = 3^2

This simplifies to:

x2x+4=9\frac{x^2}{x+4} = 9

Step 4: Solve the resulting quadratic equation

Multiply both sides by x+4x + 4 to eliminate the fraction:

x2=9(x+4)x^2 = 9(x + 4)

Expand the right-hand side:

x2=9x+36x^2 = 9x + 36

Now, bring all terms to one side:

x29x36=0x^2 - 9x - 36 = 0

Step 5: Solve the quadratic equation

We can solve this using the quadratic formula, x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}, where a=1a = 1, b=9b = -9, and c=36c = -36.

x=(9)±(9)24(1)(36)2(1)x = \frac{-(-9) \pm \sqrt{(-9)^2 - 4(1)(-36)}}{2(1)} x=9±81+1442x = \frac{9 \pm \sqrt{81 + 144}}{2} x=9±2252x = \frac{9 \pm \sqrt{225}}{2} x=9±152x = \frac{9 \pm 15}{2}

Thus, we have two solutions:

x=9+152=12orx=9152=3x = \frac{9 + 15}{2} = 12 \quad \text{or} \quad x = \frac{9 - 15}{2} = -3

Step 6: Check for extraneous solutions

Logarithms are only defined for positive arguments, so x+4>0x + 4 > 0 implies x>4x > -4. However, x=3x = -3 would make log3(3)\log_3{(-3)} undefined, so we discard x=3x = -3.

Thus, the only valid solution is:

x=12\boxed{x = 12}

Do you have any questions or would you like more details?

Here are 5 related questions:

  1. How do you solve logarithmic equations using the product and quotient rules?
  2. What happens when a logarithmic equation has no real solution?
  3. How do you determine the domain restrictions in logarithmic functions?
  4. Can you explain how to solve a system involving exponential and logarithmic equations?
  5. How does the quadratic formula work, and when is it used?

Tip: Always check if your solution is valid by substituting back into the original logarithmic equation, especially when dealing with logarithms.

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Math Problem Analysis

Mathematical Concepts

Logarithms
Quadratic Equations
Exponential Equations

Formulas

Power rule of logarithms: log_b(A^n) = n*log_b(A)
Quotient rule of logarithms: log_b(A) - log_b(B) = log_b(A/B)
Quadratic formula: x = (-b ± √(b² - 4ac)) / 2a

Theorems

Properties of logarithms
Quadratic formula
Exponential and logarithmic relationship

Suitable Grade Level

Grades 10-12