Turn on thread page Beta
    • Thread Starter

    The straight line with equation x+y=2 crosses the curve with equation y=3lnx, x > 0, at the point P.

    (a) Show that the x-coordinate of P satisfies the equation x = e^(2-x/3)

    Done that.

    An approximation to the solution of this equation is to be found using the iterative formula

    xn+1 = e^(2-xn/3), x0=1 (Sorry for bad formatting)

    (b) Write down the values of x1 and x2, giving your answers to 5 significant figures.


    (c) Show sufficient working to prove that the x-coordinate of P is 1.274, correct to 4 s.f.

    Not sure how to go about doing part (c). Don't I need to sub in x as 1.2735 and 1.2745? Not sure where to sub that in to.

    (Original post by Dan___V)
    Not sure how to go about doing part (c). Don't I need to sub in x as 1.2735 and 1.2745? Not sure where to sub that in to.
    If you have any (*) function f, and f changes sign between a and b (i.e. f(a)f(b) < 0), then f(x) has a root between a and b.

    In this case, define f(x) = x - e^(2-x/3), a = 1.2735, b = 1.2745

    (*) Well, f has to be continuous, but I *think* you can take this as a given at A-level.
Submit reply
Turn on thread page Beta
Updated: October 26, 2017

University open days

  1. University of Bradford
    University-wide Postgraduate
    Wed, 25 Jul '18
  2. University of Buckingham
    Psychology Taster Tutorial Undergraduate
    Wed, 25 Jul '18
  3. Bournemouth University
    Clearing Campus Visit Undergraduate
    Wed, 1 Aug '18
How are you feeling in the run-up to Results Day 2018?
Useful resources

Make your revision easier


Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here


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