Newtons Method

**Luck of the Irish** · May 6th 2009, 09:14 AM

I need a little help solving this problem by using newtons method:

Find x where y=6e^-x+6e^-2x+106e^-3x

**Showcase_22** · May 6th 2009, 12:05 PM

Do we have to rearrange it to make x the subject or does y equal something?

**Spec** · May 6th 2009, 01:05 PM

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 $x_0 = 4$

**Twig** · May 6th 2009, 01:09 PM

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

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

**Spec** · May 6th 2009, 01:17 PM

Right, good catch.

**Luck of the Irish** · May 6th 2009, 08:41 PM

so apply that formula and im good?

**Twig** · May 7th 2009, 11:43 AM

You might have to do a few iterations to get close enough to the solution.

**HallsofIvy** · May 7th 2009, 02:07 PM

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.

Thread: Newtons Method