Join TSR now and get all your revision questions answeredSign up now

what do i do to find k

    • Thread Starter
    Offline

    2
    ReputationRep:
    The equation f(t)=ke^t, where k>0, has one real solution.
    Find the value of k.

    I tried working it out and couldn't do it. Then I plotted it on a graph and saw that the only time there was a root (as far as I could tell), was when k=0 which had infinite roots as well as k not being positive.
    Offline

    3
    (Original post by KloppOClock)
    The equation f(t)=ke^t, where k>0, has one real solution.
    Find the value of k.

    I tried working it out and couldn't do it. Then I plotted it on a graph and saw that the only time there was a root (as far as I could tell), was when k=0 which had infinite roots as well as k not being positive.
    As it stands you just have a function. You need to equate it to something to get an equation that can be solved. You need to check the exact wording of your original question. Or post a link/photo.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by ghostwalker)
    As it stands you just have a function. You need to equate it to something to get an equation that can be solved. You need to check the exact wording of your original question. Or post a link/photo.
    Name:  stuck.jpg
Views: 16
Size:  67.2 KB
    Offline

    3
    ReputationRep:
    (Original post by KloppOClock)
    Name:  stuck.jpg
Views: 16
Size:  67.2 KB
    This is definitely the whole question? There aren't any earlier parts where f(t) is defined? Because that question doesn't make any sense- you need more information.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by sindyscape62)
    This is definitely the whole question? There aren't any earlier parts where f(t) is defined? Because that question doesn't make any sense- you need more information.
    Name:  erm.png
Views: 22
Size:  30.8 KB
    Offline

    3
    ReputationRep:
    (Original post by KloppOClock)
    Name:  erm.png
Views: 22
Size:  30.8 KB
    Ok, now it's solvable- do you see why? Part c puts f(t) equal to something else, so if you don't know what f(t) is (defined at the start) you can't get anywhere with it.

    Your first step is to write  3-2e^-^t=ke^t
    Then solve it for t. Try multiplying through by  e^t and you should get a quadratic. Quadratics either produce 0, 1 or 2 different real roots- think about the condition for a quadratic to produce just one. This will give you a solvable equation in terms of k.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by sindyscape62)
    Ok, now it's solvable- do you see why? Part c puts f(t) equal to something else, so if you don't know what f(t) is (defined at the start) you can't get anywhere with it.

    Your first step is to write  3-2e^-^t=ke^t
    Then solve it for t. Try multiplying through by  e^t and you should get a quadratic. Quadratics either produce 0, 1 or 2 different real roots- think about the condition for a quadratic to produce just one. This will give you a solvable equation in terms of k.
    oh right i forgot about the original fx bit, thanks
 
 
 
Poll
Which party will you be voting for in the General Election 2017?
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

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