# Differential Equation QuestionWatch

Thread starter 8 years ago
#1
Right I was doing a past paper, and I'm confused as how the mark scheme rearranged a certain equation. I got 5/6 marks available, but the final step lost me a mark.

How would I get from t=(1/k)ln(20/(20-kV)) to V = 20/k - (20/k)*e^-kt

I don't know how to use latex, sorry... I hope the above makes sense without it.
0
8 years ago
#2
(Original post by v1oXx-)
Right I was doing a past paper, and I'm confused as how the mark scheme rearranged a certain equation. I got 5/6 marks available, but the final step lost me a mark.

How would I get from t=(1/k)ln(20/(20-kV)) to V = 20/k - (20/k)*e^-kt

I don't know how to use latex, sorry... I hope the above makes sense without it.

Write the whole log as one i.e. ln(20/20-kv)^(1/k) = t and then write e^t = (20/20-kv)^(1/k)

Then it should be easy, hope this helps
0
Thread starter 8 years ago
#3
I did that, but then what?
0
8 years ago
#4
(Original post by v1oXx-)
I did that, but then what?
from you original question write
using log rules

Can you now rearrange for V?
0
8 years ago
#5
(Original post by v1oXx-)
I did that, but then what?
Then multiply the indices be k on both sides i.e.

e^kt = (20/20-kv)^(1/k)*(k)

Then flip both sides to get e^-kt

e^-kt = (20-kv/20k)

Then it should be easy
0
X

new posts
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### University open days

• University of East Anglia
All Departments Open 13:00-17:00. Find out more about our diverse range of subject areas and career progression in the Arts & Humanities, Social Sciences, Medicine & Health Sciences, and the Sciences. Postgraduate
Wed, 30 Jan '19
• Solent University
Careers in maritime Undergraduate
Sat, 2 Feb '19
• Sheffield Hallam University
City and Collegiate Campus Undergraduate
Sun, 3 Feb '19

### Poll

Join the discussion

#### Do you have a role model?

Yes - I know them personally (293)
26.11%
Yes - they're famous (283)
25.22%
No I don't (546)
48.66%