The problem asks to evaluate the expression $\log_8 256 + \log_8 4 - \log_8 7 + \log_8 224$ using the laws of logarithms.

AlgebraLogarithmsLogarithmic PropertiesExponent Rules
2025/4/23

1. Problem Description

The problem asks to evaluate the expression log8256+log84log87+log8224\log_8 256 + \log_8 4 - \log_8 7 + \log_8 224 using the laws of logarithms.

2. Solution Steps

We can use the properties of logarithms to simplify the expression.
First, we can use the property logax+logay=loga(xy)\log_a x + \log_a y = \log_a(xy) to combine the first two terms and the last two terms:
log8256+log84=log8(2564)=log81024\log_8 256 + \log_8 4 = \log_8(256 \cdot 4) = \log_8 1024
log87+log8224=log8(2247)=log832-\log_8 7 + \log_8 224 = \log_8(\frac{224}{7}) = \log_8 32
So the original expression becomes:
log81024+log832\log_8 1024 + \log_8 32
Using the same property again, we get:
log8(102432)=log832768\log_8 (1024 \cdot 32) = \log_8 32768
Now, we need to find xx such that 8x=327688^x = 32768.
Since 8=238 = 2^3, we can rewrite the equation as (23)x=32768(2^3)^x = 32768.
We can also write 3276832768 as 2152^{15}.
Therefore, (23)x=215(2^3)^x = 2^{15}, which means 23x=2152^{3x} = 2^{15}.
Equating the exponents, we have 3x=153x = 15, so x=5x = 5.
Therefore, log832768=5\log_8 32768 = 5.
Alternatively, we can evaluate each term separately.
log8256=log8(88/3)=log8(28)=83×log2log23=8/3\log_8 256 = \log_8 (8^{8/3}) = \log_8 (2^8) = \frac{8}{3} \times \frac{\log 2}{\log 2^3}=8/3 since 256=28=(23)8/3=88/3256 = 2^8 = (2^3)^{8/3} = 8^{8/3}. But 256=464=482256 = 4*64 = 4*8^2, so we have log8256=log8(824)=2+log84=2+log822=2+23=8/3=log8(28)=log8(88/3)\log_8 256 = \log_8(8^2 * 4) = 2 + \log_8 4 = 2 + \log_8 2^2 = 2 + \frac{2}{3} = 8/3 = log_8 (2^8) = log_8 (8^{8/3}).
Also, log84=log822=2log82=2(13)=23\log_8 4 = \log_8 2^2 = 2 \log_8 2 = 2(\frac{1}{3}) = \frac{2}{3}.
log87\log_8 7 can't be easily simplified.
log8224=log8(327)=log832+log87=log825+log87=53+log87\log_8 224 = \log_8 (32 \cdot 7) = \log_8 32 + \log_8 7 = \log_8 2^5 + \log_8 7 = \frac{5}{3} + \log_8 7.
Therefore, log8256+log84log87+log8224=83+23log87+53+log87=8+2+53=153=5\log_8 256 + \log_8 4 - \log_8 7 + \log_8 224 = \frac{8}{3} + \frac{2}{3} - \log_8 7 + \frac{5}{3} + \log_8 7 = \frac{8+2+5}{3} = \frac{15}{3} = 5.

3. Final Answer

5

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