Math Problem Statement

Find x if,log(x+5)+log(x-5)=4log2+2log3

Solution

We are given the equation:

log(x+5)+log(x5)=4log2+2log3\log(x+5) + \log(x-5) = 4\log2 + 2\log3

Step 1: Use the properties of logarithms

  1. Sum of logarithms: Apply the property loga+logb=log(ab)\log a + \log b = \log(ab) to the left-hand side: log((x+5)(x5))=4log2+2log3\log((x+5)(x-5)) = 4\log2 + 2\log3

  2. Power of logarithms: Use the property kloga=log(ak)k\log a = \log(a^k) on the right-hand side: 4log2+2log3=log(24)+log(32)=log(16)+log(9)4\log2 + 2\log3 = \log(2^4) + \log(3^2) = \log(16) + \log(9)

  3. Sum of logarithms (again): log(16)+log(9)=log(16×9)=log(144)\log(16) + \log(9) = \log(16 \times 9) = \log(144)

So, the equation becomes: log((x+5)(x5))=log(144)\log((x+5)(x-5)) = \log(144)

Step 2: Remove the logarithms

Since both sides of the equation have logarithms with the same base, we can equate the arguments: (x+5)(x5)=144(x+5)(x-5) = 144

Step 3: Expand and solve

Use the difference of squares formula on the left-hand side: x225=144x^2 - 25 = 144

Add 25 to both sides: x2=169x^2 = 169

Take the square root of both sides: x=±13x = \pm 13

Step 4: Check for valid solutions

Since log(x+5)\log(x+5) and log(x5)\log(x-5) must both be defined (i.e., their arguments must be positive):

  • If x=13x = 13, then x+5=18x+5 = 18 and x5=8x-5 = 8, which are both positive.
  • If x=13x = -13, then x+5=8x+5 = -8, which is not valid because we cannot take the logarithm of a negative number.

Thus, the only valid solution is: x=13x = 13

Let me know if you'd like any further details or clarification!

Here are some related questions you might be interested in:

  1. How can the properties of logarithms simplify other equations?
  2. What is the difference of squares formula, and how is it applied?
  3. Can you solve logarithmic equations where the bases are different?
  4. How would the equation change if one side had a natural logarithm (ln\ln)?
  5. What happens if xx takes negative values in logarithmic functions?

Tip: When solving logarithmic equations, always check if the arguments of the logarithms are positive to ensure the solution is valid!

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Math Problem Analysis

Mathematical Concepts

Logarithms
Algebra
Properties of Logarithms
Quadratic Equations

Formulas

log(a) + log(b) = log(ab)
k * log(a) = log(a^k)
Difference of squares: (x + 5)(x - 5) = x^2 - 25

Theorems

Properties of Logarithms
Difference of Squares

Suitable Grade Level

Grades 10-12