What are the constants in the binomial series expansion for (1+mx)^-n?

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The discussion focuses on finding constants in the binomial series expansion of (1+mx)^-n, specifically determining values for m and n given the series expansion. The solution reveals that m = -4 and n = 2, leading to a coefficient for x^400 expressed as a(4)^k. Participants clarify that the coefficient of x^400 involves both the binomial coefficient and the value of m, which affects the sign of the terms. Ultimately, the coefficient simplifies to 401(4)^400, confirming the values of a and k as 401 and 400, respectively. The conversation emphasizes the importance of correctly applying the binomial theorem and understanding how the signs of terms interact.
  • #31
Simon Bridge said:
I have pretty much the same notes for you:
Therefore:
... ##-400-2+1\neq -399## check arithmetic.

You have to remember to use what you learned in previous posts when you do future ones.
These lessons all fit together.

i.e. the numerator in the last calculation can be written in a shorter way remember?
This leads to a simpler way to write the whole fraction part.

Once you've done that - you need to compare what you got with what you have to show way back in post #1. If you go reread that but you should see the pattern already.

-401... :oops: Ok.. I get it now. :P
 
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  • #32
Great - so now all you have to do is put it all together!
Remember what you are trying to show?
 
  • #33
Simon Bridge said:
Great - so now all you have to do is put it all together!
Remember what you are trying to show?
##\frac{(2)(3)(4)...(401)}{400!} (4)^{400}##

##=\frac{(1)(2)(3)(4)...(401)}{400!} 4^{400}##
##=\frac{(401!)}{400!} 4^{400}##
##=\frac{(401)(400!)}{400!} 4^{400}##
##=401 (4)^{400}##

##a=401, k=400##
 
  • #34
sooyong94 said:
##\frac{(2)(3)(4)...(401)}{400!} (4)^{400}##

##=\frac{(1)(2)(3)(4)...(401)}{400!} 4^{400}##
##=\frac{(401!)}{400!} 4^{400}##
##=\frac{(401)(400!)}{400!} 4^{400}##
##=401 (4)^{400}##

##a=401, k=400##
That's it.
 
  • #35
Beautiful - pour yourself a drink!
 

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