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Bunuel
If ab ≠ 0, does a = b?

(1) x^a = x^b
(2) x = x^2


we have both possibilities a could equal b but not necessarily...we can see that x=1 because only 1=1^2....now if we know that x=1 then a and be can be any positive integers and condition x^a = x^b will still be satisfied...and they can also be equal to each other....of course x can be zero and then again both cases are possible same as for x=1, a and b can or not be equal
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Statement 1 states:

x^a=x^b
Why can we not get rid of the base x, as it is the same on both sides and say a=b?

Edit: Bunuel you are a GMAT Angel! <3
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Statement 1 states:

x^a=x^b
Why can we not get rid of the base x, as it is the same on both sides and say a=b?

Remember we can automatically equate the exponents of equal bases when that base does not equal 0, 1 or -1:

\(1^a = 1^b\), for any values of a and b (they are not necessarily equal);
\((-1)^a = (-1)^b\), for any even values of a and b (they are not necessarily equal);
\(0^a = 0^b\), for any non-zero a and b (they are not necessarily equal).
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This question has been discussed before on the forums but I do not understand why the "Solving Exponential Equations with the Same Base" rule does not hold in this follow example:

If ab ≠ 0, does a=b?

(1) x^a = x^b
(2) x = x^2

______________________________

RULE: Solving Exponential Equations with the Same Base: If B^M = B^N, then M = N.

FOR STATEMENT #1 Why doesn't this rule hold???? I understand if you set x=1, a=2, b=2 then a=b BUT if you set x=1, a=2, b=-2 then a≠b . I am trying to understand the logic why the above RULE doesn't apply in this particular case??

FYI: The solution to this problem according to the answer key is E based on the "plug-in numbers" technique described above.

Thanks for the help!
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coolo
This question has been discussed before on the forums but I do not understand why the "Solving Exponential Equations with the Same Base" rule does not hold in this follow example:

If ab ≠ 0, does a=b?

(1) x^a = x^b
(2) x = x^2

______________________________

RULE: Solving Exponential Equations with the Same Base: If B^M = B^N, then M = N.

FOR STATEMENT #1 Why doesn't this rule hold???? I understand if you set x=1, a=2, b=2 then a=b BUT if you set x=1, a=2, b=-2 then a≠b . I am trying to understand the logic why the above RULE doesn't apply in this particular case??

FYI: The solution to this problem according to the answer key is E based on the "plug-in numbers" technique described above.

Thanks for the help!

Your doubt is addressed here: https://gmatclub.com/forum/if-ab-0-does ... l#p2040836
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RULE: Solving Exponential Equations with the Same Base: If B^M = B^N, then M = N.

Your rule (above) requires some provisos.

For example, if 0^M = 0^N, we can't necessarily conclude that M = N
Likewise, if 1^M = 1^N, we can't necessarily conclude that M = N
Likewise, if 1^M = (-1)^N, we can't necessarily conclude that M = N. For example, M = 1 and N = 2 satisfies the given equation, but M ≠ N
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Bunuel
If ab ≠ 0, does a = b?

(1) x^a = x^b
(2) x = x^2


1) x^a=x^b -> x^a/x^b=1 -> x^(a-b)=1^1=1^0. Now, a-b=1 -> a ≠ b (No) and a-b=0 -> a = b (Yes). Not sufficient.
2) x = x^2 - Not sufficient as we don't know about a and b.

1)+2) putting x=x^2 in 1)
x^2a=x^2b -> x^2a/x^2b -> x^(2a-2b)=1^1=1^0, so 2a-2b=1 -> a ≠ b (No) and 2a-2b=0 -> a=b (Yes)

Together not sufficient.

Answer: (E).
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I) x^a=x^b
If x=zero
Then equation holds but we can't say whether a=b or not
Both cases hold
So insufficient

II) x^2-x=0
x(x-1)=0
x=0 or x=1
Insufficient as no info about a And b

Combining both
X can be zero or 1 in either case
Equation holds and a and b can have any value without changing result of equation so not sufficient
E is answer

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