Excel question

[Guest]

I have an equation in which i want to solve for a variable that is contained
in both a linear function and a natural log function. I have been told I
need to use Newtons method but dont know how to do this. Can anybody help?

 

[Bernard Liengme]

Explaining Newton's method would take too long.
Try a numerical analysis textbook (or get a copy of my book Excel for Sci &
Engineers)
You might be able to solve your problem with Solver but you need to do some
work first.
best wishes

 

[Jay]

I have an equation in which i want to solve for a variable that is

contained in both a linear function and a natural log function. I
have been told I need to use Newtons method but dont know how to do
this. Can anybody help?

Excel's "Goal Seek" feature is sometimes useful in solving equations.

For example, suppose you wanted to solve:
X - 10 * LN(X) = 0
for X.

In A1 put 1 (one) as a first guess at the answer.

In B1, put
=A1-10*LN(A1)

Then click
Tools >> Goal Seek
and use
Set cell: B1
To value 0 (zero)
By changing cell: A1

The answer will appear in A1. A number close to zero will appear in B1 (not
always exactly zero because of precision limits).

Behind the scenes, Excel uses some kind of iteration. Newton's method is
one kind of iteration, but I don't know if Excel uses it.