Tuesday, 23 July 2013

proof writing - Proving sequence statement using mathematical induction, dn=frac2n!



I'm stuck on this homework problem. I must prove the statement using mathematical induction




Given: A sequence d1,d2,d3,... is defined by letting d1=2 and for all integers k 2.
dk=dk1k



Show that for all integers n1 , dn=2n!







Here's my work:



Proof (by mathematical induction). For the given statement, let the property p(n) be the equation:



dn=2n!



Show that P(1) is true:
The left hand side of P(1) is dn , which equals 2 by definition of the sequence.

The right hand side is:



2(1)!=2



Show for all integers k1, if P(k) is true, then p(k+1) is true.
Let k be any integer with k1, and suppose P(k) is true. That is, suppose: (This is the inductive hypothesis)



dk=2k!



We must show that P(K+1) is true. That is, we must show that:




dk+1=2(k+1)!



(I thought I was good until here.)



But the left hand side of P(k+1) is:



dk+1=dkk+1



By inductive hypothesis:




dk+1=(22!)k+1



dk+1=22!1k+1



but that doesn't seem to equal what I needed to prove: dn=2n!


Answer



The following is not true dk+1=(22!)k+1 since dk=2k! not 22!, you actually have dk+1=(2k!)k+1=(2k!(k+1))1=2(k+1)!


No comments:

Post a Comment

real analysis - How to find limhrightarrow0fracsin(ha)h

How to find limh0sin(ha)h without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...