Solve log₉(74) + log₉(1/2): Logarithm Addition Problem

Logarithm Properties with Product Rule

log974+log912= \log_974+\log_9\frac{1}{2}=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:05 We'll use the formula for adding logarithms
00:11 We'll use this formula in our exercise
00:16 Note that the bases are equal
00:31 Let's calculate the parentheses
00:38 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

log974+log912= \log_974+\log_9\frac{1}{2}=

2

Step-by-step solution

To solve this problem, we'll apply the following steps:

  • Step 1: Identify given logarithms and their base.
  • Step 2: Employ the sum of logarithms property to combine the terms.
  • Step 3: Calculate the resulting argument of the logarithm.

Now, let's work through each step:

Step 1: We have two logarithms: log974\log_9 74 and log912\log_9 \frac{1}{2}, sharing the base of 99.

Step 2: Since the bases are the same, we use the sum property of logarithms:

log974+log912=log9(74×12)\log_9 74 + \log_9 \frac{1}{2} = \log_9 (74 \times \frac{1}{2}).

Step 3: Calculate the product 74×1274 \times \frac{1}{2}:

74×12=3774 \times \frac{1}{2} = 37.

So, we have:

log9(74×12)=log937\log_9 (74 \times \frac{1}{2}) = \log_9 37.

Therefore, the solution to the problem is log937\log_9 37.

3

Final Answer

log937 \log_937

Key Points to Remember

Essential concepts to master this topic
  • Property: Addition of logarithms equals logarithm of their product
  • Technique: log974+log912=log9(74×12) \log_9 74 + \log_9 \frac{1}{2} = \log_9(74 \times \frac{1}{2})
  • Check: Calculate product first: 74×12=37 74 \times \frac{1}{2} = 37

Common Mistakes

Avoid these frequent errors
  • Adding the arguments instead of multiplying them
    Don't add 74 + 1/2 = 74.5 inside the logarithm! This ignores the logarithm addition rule and gives log₉(74.5) instead of the correct answer. Always multiply the arguments when adding logarithms with the same base.

Practice Quiz

Test your knowledge with interactive questions

\( \log_75-\log_72= \)

FAQ

Everything you need to know about this question

Why do we multiply the numbers inside the logs when we're adding the logs?

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This comes from the logarithm property: logbx+logby=logb(x×y) \log_b x + \log_b y = \log_b(x \times y) . Think of it as the reverse of how multiplication becomes addition in logs!

What if the bases were different?

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If the bases are different, you cannot use this property directly. You would need to convert to the same base first using change of base formula.

How do I multiply 74 by 1/2?

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Multiplying by 12 \frac{1}{2} is the same as dividing by 2. So 74×12=742=37 74 \times \frac{1}{2} = \frac{74}{2} = 37 .

Can I use this rule with subtraction too?

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Yes! logbxlogby=logb(xy) \log_b x - \log_b y = \log_b(\frac{x}{y}) . Subtracting logs means dividing their arguments.

What if one of the arguments is negative?

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Be careful! Logarithms are only defined for positive numbers. If you get a negative argument, check your work - there might be an error.

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