# Newtons Method

• May 6th 2009, 09:14 AM
Luck of the Irish
Newtons Method
I need a little help solving this problem by using newtons method:

Find x where y=6e^-x+6e^-2x+106e^-3x
• May 6th 2009, 12:05 PM
Showcase_22
Do we have to rearrange it to make x the subject or does y equal something?
• May 6th 2009, 01:05 PM
Spec
I'm guessing it's $y=f(x)$, so we use Newton-Raphson's method to find the root.

$x_{n+1}=x_n - \frac{f'(x_n)}{f(x_n)}$

Try using $x_0 = 4$
• May 6th 2009, 01:09 PM
Twig
Quote:

Originally Posted by Spec
I'm guessing it's $y=f(x)$, so we use Newton-Raphson's method to find the root.

$x_{n+1}=x_n - \frac{f'(x_n)}{f(x_n)}$

Try using $x_0 = 4$

Actually its

$x_{n+1}=x_{n} - \frac{f(x_{n})}{f'(x_{n})}$
• May 6th 2009, 01:17 PM
Spec
Right, good catch.
• May 6th 2009, 08:41 PM
Luck of the Irish
so apply that formula and im good?
• May 7th 2009, 11:43 AM
Twig
You might have to do a few iterations to get close enough to the solution.
• May 7th 2009, 02:07 PM
HallsofIvy
Quote:

Originally Posted by Luck of the Irish
so apply that formula and im good?

Yes, assuming that the problem is to solve the equation 6e^-x+6e^-2x+106e^-3x= 0. You never have said that.