Hey there! Sign in to join this conversationNew here? Join for free

applying differential equations to real-life problems watch

    Offline

    22
    ReputationRep:
    (Original post by Alen.m)
    So basically it's a graph of y=30000-20000e^0.2tIn(0.9)? The reason im asking is because the text book stated it's a graph of e^0.2In(0.9t) which should definetely be different Attachment 511585511587
    It's sloppy notation on their part, what they mean is e^{0.2 \ln (0.9) t}
    • Thread Starter
    Offline

    8
    ReputationRep:
    (Original post by Zacken)
    It's sloppy notation on their part, what they mean is e^{0.2 \ln (0.9) t}
    how about if i wanna sketch the graph of y=30000-20000e^0.2In(0.9t), in this case actually as t increases the value of e^0.2In(0.9t) increases as well therefore the value of c will decrease and the graph would look like something like this?
    Attached Images
     
    Offline

    22
    ReputationRep:
    (Original post by Alen.m)
    how about if i wanna sketch the graph of y=30000-20000e^0.2In(0.9t), in this case actually as t increases the value of e^0.2In(0.9t) increases as well therefore the value of c will decrease and the graph would look like something like this?
    Not quite, if you wanted to sketch that graph, as soon as t > 1.12, the value for the exponential becomes positive, which makes 20 000 e^{\text{blah}} >> 30,000 so your whole thing becomes negative. It would look like this:

    • Thread Starter
    Offline

    8
    ReputationRep:
    (Original post by Zacken)
    Not quite, if you wanted to sketch that graph, as soon as t > 1.12, the value for the exponential becomes positive, which makes 20 000 e^{\text{blah}} >> 30,000 so your whole thing becomes negative. It would look like this:

    thanks
    • Thread Starter
    Offline

    8
    ReputationRep:
    (Original post by Zacken)
    Not quite, if you wanted to sketch that graph, as soon as t > 1.12, the value for the exponential becomes positive, which makes 20 000 e^{\text{blah}} >> 30,000 so your whole thing becomes negative. It would look like this:

    how about before 1.12 tho? the value of c getting smaller and smaller until t reaches 1.12 then it gets negative ?
    Offline

    22
    ReputationRep:
    (Original post by Alen.m)
    how about before 1.12 tho? the value of c getting smaller and smaller until t reaches 1.12 then it gets negative ?
    Yep.
    • Thread Starter
    Offline

    8
    ReputationRep:
    (Original post by Zacken)
    Yep.
    Shouldnt it be something like this tho? Coz c start getting negative as t reaches 1.12 but on yours c is already negative before 1.12 Name:  image.jpg
Views: 25
Size:  295.4 KB
    Offline

    22
    ReputationRep:
    (Original post by Alen.m)
    Shouldnt it be something like this tho? Coz c start getting negative as t reaches 1.12 but on yours c is already negative before 1.12 Name:  image.jpg
Views: 25
Size:  295.4 KB
    That's correct. Look at the scale of my graph. :-)
 
 
 
Poll
Do you agree with the PM's proposal to cut tuition fees for some courses?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.