Expanding ln isn't working for me

In summary, the conversation discusses the process of solving for x in an equation involving natural logarithms. The first method, raising the equation to the power of e, results in the correct answer. However, when expanding the logarithms and solving for x, the correct answer is not obtained. This is due to the fact that taking the exponent of a sum of natural logarithms does not cancel out the logarithms in each term.
  • #1
iScience
466
5
original equation: ln(0.2048x[itex]\frac{5}{2}[/itex])= -[itex]\frac{5}{2}[/itex]

when i just raise this to e i get..

0.2048T[itex]\frac{5}{2}[/itex]= -[itex]\frac{5}{2}[/itex]

and then i can solve for x and get the right answer. but when i expand the logs..

ln(0.2048) + [itex]\frac{5}{2}[/itex]ln(x)= -[itex]\frac{5}{2}[/itex]

0.2048+[itex]\frac{5}{2}[/itex]x=e-[itex]\frac{5}{2}[/itex]

then i try to solve for x i don't get the right answer. what am i doing wrong?
 
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  • #2
you can't do that with a sum of ln's. Taking the exponent of both sides after expansion does not cancel out the ln in each term. You would have e^(lnA + lnB) and that does not equal A+B.
 
  • #3
oops, lol thanks
 
  • #4
no problem
 

Related to Expanding ln isn't working for me

1. Why is ln not expanding for me?

There could be several reasons why ln is not expanding for you. One possibility is that you are using the wrong syntax or format. Make sure you are using the correct mathematical notation and that you are assigning the correct variables. Another reason could be that your calculator or software is not programmed to expand ln. In this case, you may need to manually calculate the expansion using the rules of logarithms.

2. How do I expand ln correctly?

To expand ln, you can use the rules of logarithms, specifically the natural logarithm rules. These include the product rule, quotient rule, and power rule. Make sure you are following the correct steps and using the correct notation. If you are still having trouble, consult a math textbook or online resource for further guidance.

3. Can ln be expanded using a calculator?

Some calculators may have the capability to expand ln, but it ultimately depends on the specific calculator and its programming. If your calculator does not have this function, you may need to manually calculate the expansion using the rules of logarithms.

4. Is there a shortcut to expanding ln?

No, there is not a shortcut to expanding ln. The process involves following the rules of logarithms and simplifying the expression until it is fully expanded. However, with practice and familiarity with the rules, you may be able to complete the expansion more quickly.

5. What are some common mistakes when expanding ln?

Some common mistakes when expanding ln include using incorrect notation, not following the rules of logarithms correctly, and not simplifying the expression fully. It is also important to check your calculations and make sure you have not made any errors along the way. Practice and double-checking your work can help avoid these mistakes.

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