Turn on thread page Beta

differentials watch

Announcements
    • Thread Starter
    Offline

    14
    ReputationRep:
    how do I work out y" + 6y' + 10y = 20, when it doesn't completely factorise when I use the factorisation method?
    Offline

    14
    If it doesn't factorize, use the quadratic formula (or complete the square) instead...
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by Kolya)
    If it doesn't factorize, use the quadratic formula (or complete the square) instead...
    that gets -3 + i, -3 - i as solutions. then I've been told sin and cos appear in the final solution... :dunce:
    Offline

    11
    ReputationRep:
    y(x) = c_1 e^{-3 x} sin(x)+c_2 e^{-3 x} cos(x)+2

    That's what wolfram gives.
    Offline

    8
    ReputationRep:
    Check this post out

    http://www.thestudentroom.co.uk/show....php?t=1169201

    all the answers you need here
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by MikeL230)


    That's what wolfram gives.
    yes, but HOW do you get that?
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by spread_logic_not_hate)
    Check this post out

    http://www.thestudentroom.co.uk/show....php?t=1169201

    all the answers you need here
    doesn't help either
    Offline

    18
    ReputationRep:
    If you get p +/- iq as solutions to the quadratic (for real numbers p and q), then your complementary solution will always be

    e^{px}(A\sin(qx) + Bcos(qx)) for some real numbers A and B.

    If you want a cheat proof for "WHY?!!?!?!", then just sub that into your differential equation and watch it come out to 0. If you want a proper proof, look it up on Google.
    • Thread Starter
    Offline

    14
    ReputationRep:
    never mind, got help from someone else.

    thread locked.
 
 
 

University open days

  • University of Warwick
    Undergraduate Open Days Undergraduate
    Sat, 20 Oct '18
  • University of Sheffield
    Undergraduate Open Days Undergraduate
    Sat, 20 Oct '18
  • Edge Hill University
    Faculty of Health and Social Care Undergraduate
    Sat, 20 Oct '18
Poll
Who is most responsible for your success at university
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

Equations

Best calculators for A level Maths

Tips on which model to get

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.