Math Problem Statement

If (log3 4)(log4 5)(log5 6) · · · (log30 31)(log31 32) = a/b log2(3) , where a and b a positive integers with no common factors, determine the value of a + b.

Solution

We are given the product:

(log34)(log45)(log56)(log3031)(log3132)(\log_3 4)(\log_4 5)(\log_5 6) \cdots (\log_{30} 31)(\log_{31} 32)

and we need to simplify this expression and express it in the form ablog2(3)\frac{a}{b} \log_2(3), where aa and bb are coprime integers, and then find the value of a+ba + b.

Step 1: Using the Change of Base Formula

We can use the change of base formula for logarithms, which states:

logba=logcalogcb\log_b a = \frac{\log_c a}{\log_c b}

We rewrite each term logn(n+1)\log_{n}(n+1) using the natural logarithm (log\log can refer to any logarithmic base, but we'll assume it's base 10):

logn(n+1)=log(n+1)log(n)\log_n (n+1) = \frac{\log(n+1)}{\log(n)}

Thus, the product becomes:

(log34)(log45)(log56)(log3132)=log4log3×log5log4×log6log5××log32log31(\log_3 4)(\log_4 5)(\log_5 6) \cdots (\log_{31} 32) = \frac{\log 4}{\log 3} \times \frac{\log 5}{\log 4} \times \frac{\log 6}{\log 5} \times \cdots \times \frac{\log 32}{\log 31}

Step 2: Simplifying the Product

Notice that in this product, many terms cancel out. Specifically, every logn\log n in the denominator cancels with the logn\log n in the numerator of the next term. The only terms that don't cancel are log32\log 32 in the numerator and log3\log 3 in the denominator.

Thus, the entire product simplifies to:

log32log3\frac{\log 32}{\log 3}

Step 3: Expressing the Logarithms in Base 2

Now, express the logarithms in terms of base 2. We know that:

log32=log232log2=5log2(since 32=25)\log 32 = \log_2 32 \cdot \log 2 = 5 \log 2 \quad \text{(since } 32 = 2^5\text{)}

Thus:

log32log3=5log2log3\frac{\log 32}{\log 3} = \frac{5 \log 2}{\log 3}

Step 4: Comparing with ablog2(3)\frac{a}{b} \log_2(3)

We are given that this expression equals ablog23\frac{a}{b} \log_2 3, and we know that log23=log3log2\log_2 3 = \frac{\log 3}{\log 2}. So:

5log2log3=ablog2log3\frac{5 \log 2}{\log 3} = \frac{a}{b} \cdot \frac{\log 2}{\log 3}

Canceling log2log3\frac{\log 2}{\log 3} on both sides, we get:

5=ab5 = \frac{a}{b}

Thus, a=5a = 5 and b=1b = 1.

Step 5: Finding a+ba + b

Finally, a+b=5+1=6a + b = 5 + 1 = 6.

Therefore, the value of a+ba + b is:

6\boxed{6}

Would you like further details or have any questions?

Here are 5 related questions to explore:

  1. How does the change of base formula for logarithms work?
  2. What are the properties of logarithms that simplify products of log terms?
  3. How can logarithmic identities be applied in complex expressions?
  4. Can you explain how natural logarithms differ from logarithms in other bases?
  5. How do you interpret logarithmic equations in terms of exponents?

Tip: Whenever dealing with logarithmic products, consider canceling terms by rewriting the logs in a common base!

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Math Problem Analysis

Mathematical Concepts

Logarithms
Change of Base Formula
Simplification of Products

Formulas

Change of Base Formula: log_b(a) = log_c(a) / log_c(b)
Logarithmic Properties: Product and Quotient Rules

Theorems

Properties of Logarithms
Change of Base Theorem

Suitable Grade Level

Grades 10-12