Pls. Help.......Pls. Help...

a,b,c are 3 nos. such that 1 > a,b,c > 0 and a + b + c = 2

Then show that \frac{a}{(1-a)}\frac{b}{(1-b)}\frac{c}{(1-c)} ≥ 8

This may be very simple but I'm getting LHS ≤ 8 instead of ≥ 8 . I'm not able to find my mistake. So pls. help.

24 Answers

39
Dr.House ·

so thats the mistake. well there is some other method and i suggest u figure it out!

1
MATRIX ·

[219]...............

1
Kalyan Pilla ·

We R to find the minimum value of the given a/1-a~~ thing

This would happen when each of the term is minimum.

ie., a=b=c=2/3

Substituting this in the given exp gives 8.

So the value is always ≥8

39
Dr.House ·

sry i was sleeping

1
Kalyan Pilla ·

LHS >0, a,b,c R fractions!!!

11
rkrish ·

@b555.........

kahaan se lhs < 0 ?????????

lhs = {(1-a)+(1-b)+(1-c)}/3 ]3 = {3-(a+b+c)}/3 ]3 = {3-2}/3 ]3 = (1/3)3 = 1/27

11
rkrish ·

sahi hai....sry i was thinking wrong

1
Kalyan Pilla ·

1/7<2/7
2/7<6/7

dividing,

1/2<1/3

Now these R fractions

1
Kalyan Pilla ·

But wat U did isnt always true.

It can be either way.

Coz Math is fact not chance.

One exception proves the statement wrong[5]

11
rkrish ·

here
abc is a fraction and so is (1-a)(1-b)(1-c) . So I dont see any mistake in dividing !!!

11
rkrish ·

@b555 & kalyan

What about this........

1/4 < 1/2
1/6 < 1/4
--------------
(1/4)/(1/6) = 3/2

(1/2)/(1/4) = 2

3/2 < 2

1
Kalyan Pilla ·

C'mon Dude how can U do that[7][7]

See ,

1<2
2<6

Now does that mean

1/2 <1/3 [7]

Think again.......

39
Dr.House ·

well, its simple am gm use na

39
Dr.House ·

1<2 and 2<10

is 1/2<2/10 ????????

11
rkrish ·

@b555

it's a + b + c = 2

11
rkrish ·

[ (a + b + c)/3 ]3 ≥ abc

abc ≤ 8/27 ...................(1)

[ {(1-a)+(1-b)+(1-c)}/3 ]3 ≥ (1-a)(1-b)(1-c)

(1-a)(1-b)(1-c) ≤ 1/27 ....................(2)

Dividing (1) / (2) Shayad here's the mistake [12][12]

abc/(1-a)(1-b)(1-c) ≤ 8

39
Dr.House ·

well is it a+b+c=2 or a+b+c≥2 ? once check..

11
rkrish ·

dats absolutely fine.....but pata toh chale wheres the mistake so that kahin aur wahi galti na ho.

21
tapanmast Vora ·

dude 5 days b4 JEE is not da time for PROOFS,,,,,,,,,,,

RELY ON SORTCUTS

11
rkrish ·

ya i took 2/5,4/5 & 4/5 . usse i got the rite ans. but taking a,b,c i think i'm making some mistake.pata nahi kahaan.

pls. try then i'll say wat i did.

21
tapanmast Vora ·

.75,.75,.5

it cums >8 obviously

21
tapanmast Vora ·

rk take an eg na.....

11
rkrish ·

pls. solve and post soln.

11
rkrish ·

arre usi mein toh doubt hai.
I'm getting LHS ≤ 8 instead of ≥ 8 . I'm not able to find my mistake.

Your Answer

Close [X]