Math Problem Statement

solve for this with step by step solution with laws a. log 15x = log 30 b. log (3x-2)=2 c. log 9 + log (x-8)=4 d. log (x+1) = log 2x e. ln (x+2) -ln (x-7) = ln 6

Solution

Let's solve each equation step by step, using logarithmic laws. I'll explain the key steps along the way.

Problem (a):

log(15x)=log(30)\log(15x) = \log(30)

Solution:

  1. Since log(15x)=log(30)\log(15x) = \log(30), we can equate the arguments because the logs are equal: 15x=3015x = 30
  2. Divide both sides by 15: x=3015=2x = \frac{30}{15} = 2
  3. Solution: x=2x = 2.

Problem (b):

log(3x2)=2\log(3x - 2) = 2

Solution:

  1. Rewrite the equation in exponential form (using the fact that if logb(y)=a\log_b(y) = a, then y=bay = b^a): 3x2=1023x - 2 = 10^2
  2. Simplify 10210^2 to get: 3x2=1003x - 2 = 100
  3. Add 2 to both sides: 3x=1023x = 102
  4. Divide by 3: x=1023=34x = \frac{102}{3} = 34
  5. Solution: x=34x = 34.

Problem (c):

log9+log(x8)=4\log 9 + \log(x - 8) = 4

Solution:

  1. Use the product rule of logarithms: loga+logb=log(ab)\log a + \log b = \log(ab). log(9(x8))=4\log(9(x - 8)) = 4
  2. Rewrite in exponential form: 9(x8)=1049(x - 8) = 10^4
  3. Calculate 104=1000010^4 = 10000: 9(x8)=100009(x - 8) = 10000
  4. Divide by 9: x8=100009x - 8 = \frac{10000}{9}
  5. Add 8 to both sides: x=100009+8x = \frac{10000}{9} + 8
  6. Solution: x=100009+8x = \frac{10000}{9} + 8.

Problem (d):

log(x+1)=log(2x)\log(x + 1) = \log(2x)

Solution:

  1. Since log(x+1)=log(2x)\log(x + 1) = \log(2x), equate the arguments: x+1=2xx + 1 = 2x
  2. Rearrange the equation: 1=x1 = x
  3. Solution: x=1x = 1.

Problem (e):

ln(x+2)ln(x7)=ln6\ln(x + 2) - \ln(x - 7) = \ln 6

Solution:

  1. Use the quotient rule of logarithms: lnalnb=ln(ab)\ln a - \ln b = \ln\left(\frac{a}{b}\right). ln(x+2x7)=ln6\ln\left(\frac{x + 2}{x - 7}\right) = \ln 6
  2. Since ln(x+2x7)=ln6\ln\left(\frac{x + 2}{x - 7}\right) = \ln 6, equate the arguments: x+2x7=6\frac{x + 2}{x - 7} = 6
  3. Cross-multiply: x+2=6(x7)x + 2 = 6(x - 7)
  4. Expand the right side: x+2=6x42x + 2 = 6x - 42
  5. Rearrange to solve for xx: 2+42=6xx2 + 42 = 6x - x 44=5x44 = 5x
  6. Divide by 5: x=445=8.8x = \frac{44}{5} = 8.8
  7. Solution: x=8.8x = 8.8.

Let me know if you need further details on any step!

Related Questions:

  1. What are the common logarithmic properties used in problem-solving?
  2. How can you verify solutions in logarithmic equations?
  3. What happens if there is no solution for a logarithmic equation?
  4. What is the difference between logarithmic and exponential equations?
  5. Can logarithmic equations have complex solutions?

Tip:

Always check the domain of the variables in logarithmic equations to avoid undefined expressions (e.g., arguments of logs must be positive).

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Math Problem Analysis

Mathematical Concepts

Logarithms
Algebra
Logarithmic Equations

Formulas

log_a(b) = c -> b = a^c
log_a(b) + log_a(c) = log_a(bc)
log_a(b) - log_a(c) = log_a(b/c)

Theorems

Equality of Logarithmic Arguments

Suitable Grade Level

Grades 10-12