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Question Number 142085 by Rexzie last updated on 30/May/21

Proof that 1+3n<n^2  for every positive integer n≥4

Proofthat1+3n<n2foreverypositiveintegern4

Answered by MJS_new last updated on 26/May/21

it′s wrong for ((3−(√(13)))/2)≤n≤((3+(√(13)))/2)

itswrongfor3132n3+132

Answered by physicstutes last updated on 26/May/21

Thesame as proving for,   0 < n^2 −3n−1   or n^2 −3n−1 > 0   (n−(3/2))^2 −(9/4)−1 >0  (n−(3/2))^2 −((13)/4)>0  ∀ n ∈ R,  (n−(3/2))^2 ≥ 0,  but  ∀ n ∈R, ⇏  (n−(3/2))^2 −((13)/4)> 0  take the case of the the interval posted above.

Thesameasprovingfor, 0<n23n1 orn23n1>0 (n32)2941>0 (n32)2134>0 nR,(n32)20,butnR,(n32)2134>0 takethecaseofthetheintervalpostedabove.

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