# Linear Approximation

## Homework Statement

Here is a picture of the problem: http://i3.photobucket.com/albums/y62/Phio/34.jpg" [Broken]

## Homework Equations

y - f(c) = f '(c) (x - c)

## The Attempt at a Solution

1/(5+x)^1/2 = (5 + x) ^ -1/2 = (1/5)^(1/2) * (1 + x/5)^(-1/2)

I have this. But I don't know if i'm on the right track...

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HallsofIvy
Homework Helper
I don't know what you are doing! You have rewritten the formula in a couple of different ways but you seem to have made no attempt to find either f'(c) or f(c), which you need to use "y- f(c)= f'(c)(x- c)".

tiny-tim
Homework Helper
Hi Fiorella! (try using the X2 tag just above the Reply box )
1/(5+x)^1/2 = (5 + x) ^ -1/2 = (1/5)^(1/2) * (1 + x/5)^(-1/2)

I have this. But I don't know if i'm on the right track...

(I've no idea why you think "y - f(c) = f '(c) (x - c)" is relevant … but anyway:)

The answers given are clearly wrong at x = 0, f(x) = 1/√5, which does not match.

But your method is correct …

just carry on regardless! 