Factorials approximation problem

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SUMMARY

The discussion focuses on the factorial approximation problem, specifically how the expression \(\frac{(N+Q)!Q!}{(Q+1)!(N+Q-1)!}\) simplifies to \(\frac{(N+Q)}{(Q+1)}\) when both N and Q are significantly larger than 1. Participants analyze the cancellation of terms, particularly how \(Q!\) cancels with \((N+Q-1)!\) and the relationship between \((Q+1)!\) and \(Q!\). The key insight is breaking down the fractions to understand the multiplication required to transition from \(Q!\) to \((Q+1)!\) and from \((N+Q-1)!\) to \((N+Q)!\).

PREREQUISITES
  • Understanding of factorial notation and properties
  • Familiarity with limits and asymptotic analysis
  • Basic algebraic manipulation skills
  • Knowledge of combinatorial identities
NEXT STEPS
  • Study Stirling's approximation for factorials
  • Explore combinatorial proofs involving factorials
  • Learn about asymptotic behavior in mathematical analysis
  • Investigate the properties of binomial coefficients
USEFUL FOR

Students in mathematics, particularly those studying combinatorics or calculus, as well as educators looking for examples of factorial simplifications in advanced topics.

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Homework Statement


How is,

[(N+Q)!Q!]/[(Q+1)!(N+Q-1)!] equal to (N+Q)/(Q+1) when N,Q>>1 ??

It looks like the Q!/(N+Q-1)! cancels but i don't see how, I am going from my lecturers notes here.

Homework Equations





The Attempt at a Solution

 
Last edited:
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Break it up - look at the fraction as

[tex]\frac{Q!}{(Q+1)!} \cdot \frac{(N+Q)!}{(N+Q-1)!}[/tex]

For the first fraction, ask yourself "what number you would multiply [itex]Q![/itex] by to get [itex](Q+1)![/itex]"?

Do a similar analysis for the second fraction.
 

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