SOLUTION: log5-3log25+2log50

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Question 516941: log5-3log25+2log50
Answer by bucky(2189) About Me  (Show Source):
You can put this solution on YOUR website!
Given to simplify:
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log%2810%2C5%29-3%2Alog%2810%2C25%29%2B2%2Alog%2810%2C50%29
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Notice that 25=5%5E2. Substitute 5%5E2 for 25 to change the expression to:
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log%2810%2C5%29-3%2Alog%2810%2C5%5E2%29%2B2%2Alog%2810%2C50%29
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By the rules of logarithms an exponent can be brought out as the multiplier of the log term. So bring the exponent 2 out and make it the multiplier of its log term. When you do that you have:
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log%2810%2C5%29-3%2A2%2Alog%2810%2C5%29%2B2%2Alog%2810%2C50%29
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The first two terms of the expression now involve log%2810%2C5%29. Let's do the same for the last term. Note that 50+=+5%2A10. So in the last term, replace 50 by 5%2A10 to get:
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log%2810%2C5%29-3%2A2%2Alog%2810%2C5%29%2B2%2Alog%2810%2C5%2A10%29
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By the rules of logarithms, the log of a product is equal to the sum of the logs of the two multipliers. So the last term can be changed as follows:
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log%2810%2C5%29-3%2A2%2Alog%2810%2C5%29%2B2%2A%28log%2810%2C5%29%2Blog%2810%2C10%29%29
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Do the distributed multiplication of the last term by multiplying the 2 times each of the two log terms in the parentheses:
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log%2810%2C5%29-3%2A2%2Alog%2810%2C5%29%2B2%2Alog%2810%2C5%29%2B2%2Alog%2810%2C10%29
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The log%2810%2C10%29 term means to what power do you have to raise 10 (the base) to make it equal 10? The answer to that is the power of 1. So log%2810%2C10%29 is equal to 1. Substitute 1 for log%2810%2C10%29 and the expression becomes:
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log%2810%2C5%29-3%2A2%2Alog%2810%2C5%29%2B2%2Alog%2810%2C5%29%2B2%2A1
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Do the multiplications of the constants in the second and last terms and the expression becomes:
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log%2810%2C5%29-6%2Alog%2810%2C5%29%2B2%2Alog%2810%2C5%29%2B2
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Add together the terms containing log%2810%2C5%29 which is %281-6%2B2%29%2Alog%2810%2C5%29 and the expression becomes:
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-3%2Alog%2810%2C5%29%2B+2
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And that's the expression that results from simplifying the expression that you originally were given.
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Keep in mind that log%2810%2C5%29 is just a number that you can look up on a calculator. If you enter 5 and press the log key, you will get the value 0.698970004. Substitute this for log%2810%2C+5%29 and the answer transforms to:
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-3%2A0.698970004%2B+2
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Multiply out the first term and then add the 2 and it becomes:
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-2.096910013%2B2
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Which adds up to be:
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-0.096910013
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And this is the numerical solution to this problem.
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Hope this helps you to understand logarithm operations a little better.
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