- #1
Appleton
- 91
- 0
Expand the following functions as a series of ascending powers of x up to and including the term x^3. In each case give the range of values of x for which the expansion is valid.
(1+(1/x))^(-1)
1 + (-1)(1/x) + (-1)(-2)(1/x^2)/2 + (-1)(-2)(-3)(1/x^3)/3!
= 1 - (1/x) + (1/x^2) - (1/x^3)
-1< 1/x <1
x<-1 and x>1
Which is invalid, but I can't see why. The way I deduced the ranges of values of x wasn't very rigorous so I suspect that might have something to do with it.
]
(1+(1/x))^(-1)
The Attempt at a Solution
1 + (-1)(1/x) + (-1)(-2)(1/x^2)/2 + (-1)(-2)(-3)(1/x^3)/3!
= 1 - (1/x) + (1/x^2) - (1/x^3)
-1< 1/x <1
x<-1 and x>1
Which is invalid, but I can't see why. The way I deduced the ranges of values of x wasn't very rigorous so I suspect that might have something to do with it.
]