very very easy

Prove that 2mn> mn as well as nm

Find the shortest proof.

HINT: this is in syllabus

oops sry, condition: n,m>0 and ε N

13 Answers

9
Celestine preetham ·

see with m=2 n=0

there are some conditions missing

24
eureka123 ·

yeah cele is rite...some cond is missing

WARNING:Long method.....(but did it just to check validity of question)

considering m,n>0
take log both sides
mn.log2>nlogm
=> n(mlog2-logm)>0
Since n>0 so (mlog2-logm) must be greater than 0

consider f(m)=p=mlog2-logm
p'=log2-1/m
=>p changes sign at m=1/log2

so the question should be true for m>1/log2 and n>0

106
Asish Mahapatra ·

edited question:
m,n ε N

11
virang1 Jhaveri ·

See Easy
2mn>mn
rite
Now you cancel n on both the sides
Therefore
2m>m
This is understandable therefore done

1
Akand ·

wel...
to prove 2mn>mn
to prove 2m>m
to prove 2>m1/m

and isnt it obvious 2>m1/m????

in d same way....

to prove 2mn>nm
to prove 2n>n
to prove 2>n1/n........

1
Akand ·

waaaaaaaahhhhh virang.u posted while i was typing.....

1
Akand ·

so lets see who will prove first.........

2m>m

lets prove this.

1
Akand ·

2m>m
mlog2>logm
m>logm/log2

or by taking

2>m1/m
then take AM GM inequalities..

9
Celestine preetham ·

it boils down to

2m>m

now m=1 is true

consider a function 2m -m f'(x) = ln2.2m - 1

this f'(x) > 0 for mε N

so its a strictly inc function

has m=1 is already true
its true for all mε N

1
Akand ·

or.................
we cud do by PMI
2m>m
for f(1) 2>1 so f(k) is true
let f(k) be true so..
2k>k
now we need to prove f(k+1) is true
LHS..2k+1=2k.2
>k.2
>K+1

so f(k+1) is also true

so by induction...

2m>m

106
Asish Mahapatra ·

easiest proof:

consider a set A having n distinct elements and set B having m distinct elements

No. of relations from A→B = 2mn
No. of functions from A→B = mn

As No. of relations < No. of functions so 2mn>mn
similarly taking A has m elements and B has n elements it can be proved that
2mn>nm

9
Celestine preetham ·

but asish the human mind isnt framed to think in terms of #12

may be the Q setter worked backwards !!!!

9
Celestine preetham ·

eureka sorry i dint see that

#3 is = #10

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