SOLUTION: Hello everyone, I am doing some problems on logarithms but was struggling with a couple of them. I will post them one at a time like the rules mandate. Suppose that x=ln(A) and

Algebra ->  Logarithm Solvers, Trainers and Word Problems -> SOLUTION: Hello everyone, I am doing some problems on logarithms but was struggling with a couple of them. I will post them one at a time like the rules mandate. Suppose that x=ln(A) and       Log On


   



Question 1203523: Hello everyone, I am doing some problems on logarithms but was struggling with a couple of them. I will post them one at a time like the rules mandate.
Suppose that x=ln(A) and y=ln(B). Write the following expression in terms of x and y (so there won't be an A or B).
ln(A^5 * squareroot B)=?

Found 3 solutions by MathLover1, ikleyn, josgarithmetic:
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

Suppose that
+x=ln%28A%29++
+y=ln%28B%29+
Write the following expression in terms of +x+ and +y+ (so there won't be an +A+or+%7B%7B%7B+B+).
+ln%28A%5E5+%2A+sqrt+%28B%29%29+=?


+x=ln%28A%29++=> +A+=+e%5Ex++
+y=ln%28B%29+=> +B=e%5Ey+

then substitute in +ln%28A%5E5+%2A+sqrt+%28B%29%29+

+ln%28%28e%5Ex%29%5E5+%2A+sqrt+%28e%5Ey%29%29+
=+ln%28%28e%5E5x%29+%2A+%28e%5Ey%29%5E%281%2F2%29%29+
=+ln%28%28e%5E%285x+%2By%2F2%29%29%29+
=+5x+%2B+y%2F2+=> answer


Answer by ikleyn(52880) About Me  (Show Source):
You can put this solution on YOUR website!
.
Hello everyone, I am doing some problems on logarithms but was struggling with a couple of them.
I will post them one at a time like the rules mandate.
Suppose that x=ln(A) and y=ln(B). Write the following expression in terms of x and y (so there won't be an A or B).
ln(A^5 * squareroot B)=?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

They want you learn and use the basic rules of logarithms 

    ln(p*q) = ln(p) + ln(q),

    ln(p^n) = n*ln(p).


It is true not only for the natural logarithms, but for any other logarithm bases, too.


So, in this case, the solution is in one single line

    ln%28A%5E5%2Asqrt%28B%29%29 = ln%28A%5E5%29 + ln%28sqrt%28B%29%29 = 5*ln(A) + %281%2F2%29%2Aln%28B%29 = 5x + %281%2F2%29y.    ANSWER

Solved.

---------------

There is no any need to make writing longer.

Some tutors at this forum think that the longer their writing is - the better their solutions look like
- the smarter they are looking, themselves.

Although in Math, everything is exactly in reversed order - nothing in writing should be longer than it should be.


        Only because of it,  Math is beautiful as an art,
                and is not so terrible as a swamp.


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On logarithms and their properties,  see these introductory lessons
    - WHAT IS the logarithm
    - Properties of the logarithm
    - Change of Base Formula for logarithms
    - Evaluate logarithms without using a calculator
    - Simplifying expressions with logarithms
    - Solving logarithmic equations
in this site.



Answer by josgarithmetic(39630) About Me  (Show Source):
You can put this solution on YOUR website!
ln%28A%5E5%2Asqrt%28B%29%29
ln%28A%5E5%29%2Bln%28sqrt%28B%29%29
5%2Aln%28A%29%2Bln%28B%5E%280.5%29%29
5%2Aln%28A%29%2B0.5%2Aln%28B%29
now simply substitute the given expression equivalences.

5x%2B0.5y