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Tewodros Amdeberhan DeVry Institute, Mathematics
 

Summary: Tewodros Amdeberhan
DeVry Institute, Mathematics
630 US Highway One, North Brunswick, NJ 08902
amdberhan@admin.nj.devry.edu
Problem 1540: P
a Show that x
n + x ,1n ,x + 1n has a unique non-zero real root rn.
b Show that rn increases monotonically.
c Evaluate limn!1 rn=n:
Solution: Let fnx := x
n + x ,1n ,x + 1n. Notice that if x = ,t 0, then we have
fn,t = ,1n
t
n
+ t + 1n
,t ,1n
is either always positive or negative depending on n. Thus it su ces to look for the positive roots
of the fn's.
Claim: 9! rn 0 such that fnx 0 for 0 x rn; fnx 0 for x rn; fnrn = 0 and
rn rn,1.

  

Source: Amdeberhan, Tewodros - Department of Mathematics, Tulane University

 

Collections: Mathematics