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If log⁡1281=p\log_{12}81 = p, then 34−p4+p3\frac{4-p}{4+p} is equal to

Solution

✅ Correct Option: 3

Given: log⁡1281=p\log_{12}81 = p

To find: 34−p4+p3\frac{4-p}{4+p}


First, let's recognize that 81=3481 = 3^4 (since 3×3×3×3=813 \times 3 \times 3 \times 3 = 81).

So: log⁡1281=log⁡1234=p\log_{12}81 = \log_{12}3^4 = p

Using the power rule of logarithms: log⁡a(xn)=nlog⁡a(x)\log_a(x^n) = n\log_a(x)

log⁡1234=4log⁡123=p\log_{12}3^4 = 4\log_{12}3 = p

Therefore: log⁡123=p4\log_{12}3 = \frac{p}{4}


Now let's work on 34−p4+p3\frac{4-p}{4+p}.

Since p=4log⁡123p = 4\log_{12}3, we substitute:

34−p4+p=34−4log⁡1234+4log⁡1233\frac{4-p}{4+p} = 3\frac{4 - 4\log_{12}3}{4 + 4\log_{12}3}

Factor out 4 from numerator and denominator:

=34(1−log⁡123)4(1+log⁡123)=31−log⁡1231+log⁡123= 3\frac{4(1 - \log_{12}3)}{4(1 + \log_{12}3)} = 3\frac{1 - \log_{12}3}{1 + \log_{12}3}


Here's a key insight: log⁡1212=1\log_{12}12 = 1 (since any number to the power 1 equals itself).

So we can rewrite:

1=log⁡12121 = \log_{12}12

1−log⁡123=log⁡1212−log⁡1231 - \log_{12}3 = \log_{12}12 - \log_{12}3

1+log⁡123=log⁡1212+log⁡1231 + \log_{12}3 = \log_{12}12 + \log_{12}3


Using the quotient rule: log⁡a(x)−log⁡a(y)=log⁡a(xy)\log_a(x) - \log_a(y) = \log_a(\frac{x}{y})

And the product rule: log⁡a(x)+log⁡a(y)=log⁡a(xy)\log_a(x) + \log_a(y) = \log_a(xy)

3log⁡1212−log⁡123log⁡1212+log⁡123=3log⁡12(123)log⁡12(12×3)=3log⁡124log⁡12363\frac{\log_{12}12 - \log_{12}3}{\log_{12}12 + \log_{12}3} = 3\frac{\log_{12}(\frac{12}{3})}{\log_{12}(12 \times 3)} = 3\frac{\log_{12}4}{\log_{12}36}


The change of base formula states: log⁡a(x)log⁡a(y)=log⁡y(x)\frac{\log_a(x)}{\log_a(y)} = \log_y(x)

So: log⁡124log⁡1236=log⁡364\frac{\log_{12}4}{\log_{12}36} = \log_{36}4

Therefore: 3log⁡124log⁡1236=3log⁡3643\frac{\log_{12}4}{\log_{12}36} = 3\log_{36}4


Using alog⁡b(x)=log⁡b(xa)a\log_b(x) = \log_b(x^a):

3log⁡364=log⁡3643=log⁡36643\log_{36}4 = \log_{36}4^3 = \log_{36}64


Notice that:

36=6236 = 6^2

64=8264 = 8^2

So: log⁡3664=log⁡6282\log_{36}64 = \log_{6^2}8^2

Using the property log⁡ambn=nmlog⁡a(b)\log_{a^m}b^n = \frac{n}{m}\log_a(b):

log⁡6282=22log⁡6(8)=log⁡6(8)\log_{6^2}8^2 = \frac{2}{2}\log_6(8) = \log_6(8)


Therefore: 34−p4+p=log⁡6(8)3\frac{4-p}{4+p} = \log_6(8)

This problem beautifully demonstrates how multiple logarithm properties work together to simplify complex expressions!

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