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Re: What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x [#permalink]
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gracie wrote:
GMATPrepNow wrote:
What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x^(x² + 8x +6) ?

A) -4
B) -3
C) 3
D) 4
E) 5

* Kudos for all correct solutions


subtract exponent 2 from exponent 1
x^2-4x-12=0
x=6,-2
6+(-2)=4
D


That's close, but you haven't found all of the possible solutions.

Cheers,
Brent
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Re: What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x [#permalink]
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GMATPrepNow wrote:
gracie wrote:
GMATPrepNow wrote:
What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x^(x² + 8x +6) ?

A) -4
B) -3
C) 3
D) 4
E) 5

* Kudos for all correct solutions


subtract exponent 2 from exponent 1
x^2-4x-12=0
x=6,-2
6+(-2)=4
D


That's close, but you haven't found all of the possible solutions.

Cheers,
Brent


I see it now, should have noted that 1^0=1^15.
Add 1 to 4 and the answer is 5.
Thanks. Good problem.
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Re: What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x [#permalink]
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gracie wrote:
I see it now, should have noted that 1^0=1^15.
Add 1 to 4 and the answer is 5.
Thanks. Good problem.


Nice work.
I should also note that x = 0 is another solution (but it doesn't change the answer)

We must also check to see whether x = -1 is a possible solution.
When we plug x = -1 into the equation, we find that it is NOT a solution.

So, the solutions are x = 6, x = -2 and x = 1

Cheers,
Brent
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Re: What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x [#permalink]
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GMATPrepNow wrote:
What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x^(x² + 8x +6) ?

A) -4
B) -3
C) 3
D) 4
E) 5

* Kudos for all correct solutions


The equation can be written as -

\(x ^{(x-6)(x+2)} = 1\)

L.H.S = R.H.S, when x = 1,6,-2
Hence, Sum = 5
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Re: What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x [#permalink]
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Best approach would be to take log on both sides.

logx[(x-6)(x+2)] =0
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Re: What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x [#permalink]
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srinjoy1990 wrote:
Best approach would be to take log on both sides.

logx[(x-6)(x+2)] =0


Unfortunately, you won't have a calculator (or a log table for that day) on test day.
That said, if you did have a calculator, what values would you plug in for x?

Cheers,
Brent
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Re: What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x [#permalink]
GMATPrepNow wrote:
srinjoy1990 wrote:
Best approach would be to take log on both sides.

logx[(x-6)(x+2)] =0


Unfortunately, you won't have a calculator (or a log table for that day) on test day.
That said, if you did have a calculator, what values would you plug in for x?

Cheers,
Brent



we need not take values thats the point, we can solve the equation by taking log.

you have something like this,

logx(x^2-4x-12) = 0.

logx =0 | x^2-4x-12=0

so, roots are, x=1 , and the solution to the equation x^2-4x-12=0.

so, 5 (1+4).
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Re: What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x [#permalink]
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GMATPrepNow wrote:
What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x^(x² + 8x +6) ?

A) -4
B) -3
C) 3
D) 4
E) 5

* Kudos for all correct solutions

x^(2x² + 4x – 6) = x^(x² + 8x +6)
2x² + 4x – 6 = x² + 8x +6
x² - 4x - 12 = (x+2)(x-6)
from here x = -2 , 6
here x = 1 will also satisfy the equation
so -2+6+1 = 5
E is the answer
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Re: What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x [#permalink]
x = 1,6,-2
Sum = 5.
Hence E.

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What is the sum of all solutions to the equation x^(2x² + 4x – 6) = x [#permalink]
\(x^{(2x^2 + 4x – 6)} = x^{(x^2 + 8x +6)}\)

Bring both equations on same side and this becomes -

\(x^{(2x^2 + 4x – 6) - (x^2 + 8x +6)}\)

\(x^{(x^2 - 4x – 12)}\) = 1

Now any number to power another number is equal to 1 in 2 cases
\(n^{(0)}\) or n = 1

So, lets check both cases
Case 1 -
\(n^{(0)}\) which means => \(x^2 - 4x – 12 = 0\)
(x-6)(x+2) = 0 i.e. x = 6, -2

Case 2 -
x = 1

So sum of all -> 6-2+1 = 5
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Re: What is the sum of all solutions to the equation x^(2x² + 4x 6) = x [#permalink]
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Re: What is the sum of all solutions to the equation x^(2x² + 4x 6) = x [#permalink]
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