# Extended binomial theorem

## Homework Statement

Calculate $$\sqrt{1/20}$$ using the extended binomial theormem. (a precision of k=4 is enough)

## The Attempt at a Solution

$$\sqrt{1/20}= (1 + (-19/20) )^{1/2}= \sum( choose (1/2,k)*(-19/20)^k) = 1- 1/2*19/20-1/8*361/400+1/16*6589/8000 = 0.72...$$ is wrong.

## Homework Statement

Where is my mistake?
Thanks
Tal

vela
Staff Emeritus
Homework Helper

## Homework Statement

Calculate $$\sqrt{1/20}$$ using the extended binomial theormem. (a precision of k=4 is enough)

## The Attempt at a Solution

$$\sqrt{1/20}= (1 + (-19/20) )^{1/2}= \sum( choose (1/2,k)*(-19/20)^k) = 1- 1/2*19/20-1/8*361/400+1/16*6589/8000 = 0.72...$$ is wrong.

## Homework Statement

Where is my mistake?
Thanks
Tal
You made a simple sign mistake somewhere, it seems.