- #1
Harrisonized
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This isn't a coursework problem. I'm on winter break.
A common approximation used in physics is:
(1+x)n ≈ 1+nx for small x
This implies that
lim(x→0) (1+x)n = lim(x→0) 1+nx
which is a true statement. However,
lim(x→0) (1+x)n
= lim(x→0) [(1+x)1/x]xn
= lim(x→0) exn
This leads to the fact that
(1+x)n ≈ exn for small x
The question is: which one is a better approximation, and how do I show it?
Compute the error terms.
E1 = (1+x)n - (1+nx)
E2 = (1+x)n - exn
They intersect at E1 = E2, or at
1+nx = exn
I'm not sure how to go from here. I'm pretty sure that x can't be isolated. However, since exn is always positive, I think the only root is at x=0. Wolfram gives a funny answer though. If anyone would like to explain Wolfram's answer, please do.
http://www.wolframalpha.com/input/?i=1%2Bnx+%3D+e^%28nx%29
Assuming positive n, for a large x, exn is a worse approximation for the function. Since exn grows much faster than (1+nx), exn is always a worse approximation than (1+nx).
Assuming negative n, for a large x, exn is a worse approximation for the function. Since exn doesn't grow as quickly as (1+nx) (it levels off), exn is always a better approximation than (1+nx).
Or it may just be the case that 1+nx is always a better approximation, since it's more commonly used.
Homework Statement
A common approximation used in physics is:
(1+x)n ≈ 1+nx for small x
This implies that
lim(x→0) (1+x)n = lim(x→0) 1+nx
which is a true statement. However,
lim(x→0) (1+x)n
= lim(x→0) [(1+x)1/x]xn
= lim(x→0) exn
This leads to the fact that
(1+x)n ≈ exn for small x
The question is: which one is a better approximation, and how do I show it?
The Attempt at a Solution
Compute the error terms.
E1 = (1+x)n - (1+nx)
E2 = (1+x)n - exn
They intersect at E1 = E2, or at
1+nx = exn
I'm not sure how to go from here. I'm pretty sure that x can't be isolated. However, since exn is always positive, I think the only root is at x=0. Wolfram gives a funny answer though. If anyone would like to explain Wolfram's answer, please do.
http://www.wolframalpha.com/input/?i=1%2Bnx+%3D+e^%28nx%29
Assuming positive n, for a large x, exn is a worse approximation for the function. Since exn grows much faster than (1+nx), exn is always a worse approximation than (1+nx).
Assuming negative n, for a large x, exn is a worse approximation for the function. Since exn doesn't grow as quickly as (1+nx) (it levels off), exn is always a better approximation than (1+nx).
Or it may just be the case that 1+nx is always a better approximation, since it's more commonly used.
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