Using log rules: subtraction of ln(y+5)-lny is the same as ln((y+5)/y). Then do everything to the power of e to get rid of ln. Then you should be able to rearrange for y.

Original post by zolearns

It is given that ln(y+5)-lny=2lnx. Express y in terms of x, in a form not involving logarithms.

This is what I have so far (I can't upload a pic)

ln(y+5)-lny=lnx^2

lny+ln5-lny=lnx^2

This is what I have so far (I can't upload a pic)

ln(y+5)-lny=lnx^2

lny+ln5-lny=lnx^2

your expansion for ln(y+5) into lny+ln5 is incorrect. "lny+ln5" is ln(5y).

in this case leave the ln(y+5) as it is. logarithm law states when you subtract lns, you divide things in the function so you're supposed to do (y+5)/y. when you take e from both sides of the equations, the ln cancels out on either side and you just do simple rearranging.

Original post by h4nn4

your expansion for ln(y+5) into lny+ln5 is incorrect. "lny+ln5" is ln(5y).

in this case leave the ln(y+5) as it is. logarithm law states when you subtract lns, you divide things in the function so you're supposed to do (y+5)/y. when you take e from both sides of the equations, the ln cancels out on either side and you just do simple rearranging.

in this case leave the ln(y+5) as it is. logarithm law states when you subtract lns, you divide things in the function so you're supposed to do (y+5)/y. when you take e from both sides of the equations, the ln cancels out on either side and you just do simple rearranging.

Be careful with your language here. You don't "take e from both sides of the equation" - you either "exponentiate both sides", or equivalently, "raise e to the power of each side" In effect, you're applying the inverse function to ln.

Original post by davros

Be careful with your language here. You don't "take e from both sides of the equation" - you either "exponentiate both sides", or equivalently, "raise e to the power of each side" In effect, you're applying the inverse function to ln.

very true, thanks

- How important is maths in a-level physics?
- Getting A* in math in year 12?
- Arhenius equation chem a-level
- Edexcel AS Maths Paper 1 (Pure)
- Biology and chemistry
- Aqa a level physics
- Bristol Maths Test for Engineering Courses
- Fail to meet conditional offers in UCL
- In v=ab^t. What does b represent. Logb is the gradient I think but what is b. Thanks
- logbase e or logbase 10?
- A Level Options
- Year 2 Stats A Level Maths Question
- WJEC Unit 1 Maths As Level Discussion 15 May 2024
- GCSE Maths Tips and Tricks!
- Logs
- A-Level Further Maths Options
- regretting not doing a-level maths
- What should I choose bio or math
- Erm, can anyone decipher this math question?
- AS physics??

Latest

Trending