# Homework Help: C3 coursework

1. Jul 2, 2008

### RMHAZARD

I am on my final part of my C3 coursework, doing the comparison of methods, i have found the root using the change of sign method, and the newton raphson method but i am struggling with using the rearranging method. the equation i am using is x^3 +5x -4, i have tried rearranging it to get the root which is 0.3274, but i can not get it to converge to this figure, the coursework is due in tomorrow at 4pm and i just need to do this final bit and i am done but i can't i have been tring for 3 hours please help me.

Thanks

I am not asking for it to be done for me i am just asking to know whati need to do to my equation to get my root 0.3274.

2. Jul 3, 2008

### dirk_mec1

Show me newton-raphson with your equation.

3. Jul 3, 2008

### HallsofIvy

I have no idea what you mean by the "rearranging method". Please explain.

4. Jul 4, 2008

Hes talking about the g(x) method. You make your equation in the form x = ... then find points of interception on the graph y = x. These interceptions are the roots of the orignal equation.

You need to find a root between 2 points using a integer search. Take the x value from the search and put it in to the x = equation. then take that value and put it in to the equation again untill it converges to 5/6 DP.

eg x=x^3-2x/3
x = (-1, 0)
x0 = -1
x1 = -1^3-2*-1/3 = n
x2 = n^3-2*n/3 etc.

5. Jul 4, 2008

### HallsofIvy

What function are you talking about? x= x3- 2x/3 is equivalent to x3- (2/3)x- x= 0 or x3- (5/3)x= 0 which has NO roots between -1 and 0. The method you give will eventually converge to 0 which is a root.

6. Jul 4, 2008