Solve the Equation: 2log(x+4) = 1 | Step-by-Step Solution

Logarithmic Equations with Exponential Conversion

Calculate X:

2log(x+4)=1 2\log(x+4)=1

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find X
00:03 We'll use the logarithm of power formula, and move the 2 to the logarithm
00:13 A logarithm without a base is a logarithm with base 10
00:30 We'll use the definition of logarithm to find the solution
00:50 We'll expand brackets using short multiplication formulas
00:55 Let's arrange the equation
01:05 We'll use the roots formula to find possible solutions
01:15 Let's calculate and solve
02:05 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Calculate X:

2log(x+4)=1 2\log(x+4)=1

2

Step-by-step solution

To solve the equation 2log(x+4)=1 2\log(x+4) = 1 , we follow these steps:

  • Step 1: Divide both sides by 2 to simplify the equation.
  • Step 2: Apply the logarithm property to rewrite the equation.
  • Step 3: Convert the logarithmic equation into an exponential equation.
  • Step 4: Solve the resulting equation for x x .

Let's work through the steps:

Step 1: Start by dividing both sides of the equation by 2:

log(x+4)=12 \log(x+4) = \frac{1}{2}

Step 2: Translate the logarithmic equation to its exponential form. Recall that logb(A)=C\log_b(A) = C implies bC=Ab^C = A. Here, the base is 10 (since it's a common logarithm when the base is not specified):

x+4=1012 x+4 = 10^{\frac{1}{2}}

Step 3: Simplify 1012 10^{\frac{1}{2}} which is the square root of 10:

x+4=10 x+4 = \sqrt{10}

Step 4: Solve for x x by isolating it:

x=104 x = \sqrt{10} - 4

Thus, the value of x x is 4+10 -4 + \sqrt{10} .

3

Final Answer

4+10 -4+\sqrt{10}

Key Points to Remember

Essential concepts to master this topic
  • Property: Convert log equation to exponential form using base 10
  • Technique: log(x+4)=12 \log(x+4) = \frac{1}{2} becomes x+4=1012 x+4 = 10^{\frac{1}{2}}
  • Check: Substitute x=4+10 x = -4 + \sqrt{10} : 2log(10)=1 2\log(\sqrt{10}) = 1

Common Mistakes

Avoid these frequent errors
  • Forgetting to divide by 2 first
    Don't convert 2log(x+4)=1 2\log(x+4) = 1 directly to x+4=101 x+4 = 10^1 = wrong answer x = 6! The coefficient 2 must be handled first. Always isolate the logarithm by dividing both sides by 2 before converting to exponential form.

Practice Quiz

Test your knowledge with interactive questions

\( \log_{10}3+\log_{10}4= \)

FAQ

Everything you need to know about this question

Why do we divide by 2 before converting to exponential form?

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The equation has 2 times the logarithm, not just the logarithm itself. We need to isolate log(x+4) \log(x+4) first by dividing both sides by 2, giving us log(x+4)=12 \log(x+4) = \frac{1}{2} .

What does 1012 10^{\frac{1}{2}} equal?

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1012 10^{\frac{1}{2}} means the square root of 10, which is 10 \sqrt{10} . Any number raised to the power of 12 \frac{1}{2} equals its square root.

Why isn't the answer just 1?

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If x = 1, then 2log(1+4)=2log(5)1.4 2\log(1+4) = 2\log(5) \approx 1.4 , not 1! The equation requires exactly x=4+10 x = -4 + \sqrt{10} to make both sides equal.

How do I check if x=4+10 x = -4 + \sqrt{10} is correct?

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Substitute back: x+4=(4+10)+4=10 x + 4 = (-4 + \sqrt{10}) + 4 = \sqrt{10} . Then 2log(10)=212=1 2\log(\sqrt{10}) = 2 \cdot \frac{1}{2} = 1

What if I forgot the logarithm is base 10?

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When no base is written, it's always base 10 (common logarithm). So log(x+4)=12 \log(x+4) = \frac{1}{2} means log10(x+4)=12 \log_{10}(x+4) = \frac{1}{2} , which converts to x+4=1012 x+4 = 10^{\frac{1}{2}} .

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