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Exponents theory 2

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by metallicafan » Sun Jul 01, 2012 5:31 am
Hi,

I would like to know in which cases we can say that because a^x > a^y, then x>y.

If a is a fraction is between 0 and 1, we cannot claim that, right?

Thank you!
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Source: — Data Sufficiency |

by \'manpreet singh » Sun Jul 01, 2012 10:00 am
metallicafan wrote:Hi,

I would like to know in which cases we can say that because a^x > a^y, then x>y.

If a is a fraction is between 0 and 1, we cannot claim that, right?

Thank you!
1)for all a>1 this is true...no issues here

2)for 0<a<1
let a=0.5 0.5^1>0.5^2 here the above relation is not true as 1>2 (false)

3)for -1<a<0 again let a=-0.5
-0.5^1<-0.5^2 and 1<2...the relation holds valid here
-0.5^2>-0.5^3 but 2>3...the relation is not valid anymore

4)for a<-1 a=-2 -2^1>-2^2 but here 1>2 (which is false)hence the above relation not valid


Hence the range of 'a' for which the above relation holds true is:
a>1 for all x,y
and -1<a<0
for all odd values of x and y(definitely)

======================
manpreet

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Last edited by \'manpreet singh on Mon Jul 02, 2012 8:51 pm, edited 2 times in total.
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by jcnasia » Mon Jul 02, 2012 3:49 am
'manpreet singh wrote:
1)for all a>1 this is true...no issues here

2)for 0<a<1
let a=0.5 0.5^1>0.5^2 here the above relation is not true as 1>2 (false)

3)for -1<a<0 again let a=-0.5
-0.5^1<-0.5^2 hence 1<2...the relation holds valid here

4)for a<-1 a=-2 -2^1>-2^2 but here 1>2 (which is false)hence the above relation not valid


Hence the range of 'a' for which the above relation holds true is:
a>1 and -1<a<0
It doesn't hold true for -1 < a < 0.
For example, (-.5)^2 > (-.5)^3 but 2 < 3.
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by \'manpreet singh » Mon Jul 02, 2012 8:46 pm
jcnasia wrote:
'manpreet singh wrote:
1)for all a>1 this is true...no issues here

2)for 0<a<1
let a=0.5 0.5^1>0.5^2 here the above relation is not true as 1>2 (false)

3)for -1<a<0 again let a=-0.5
-0.5^1<-0.5^2 hence 1<2...the relation holds valid here

4)for a<-1 a=-2 -2^1>-2^2 but here 1>2 (which is false)hence the above relation not valid


Hence the range of 'a' for which the above relation holds true is:
a>1 and -1<a<0
It doesn't hold true for -1 < a < 0.
For example, (-.5)^2 > (-.5)^3 but 2 < 3.
Yes you are right, i missed on the odd even case here...

We can then generalize that it holds true for all odd values of x and y.(-1<a<0)

Made the correction in my post too.
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