# precalc

(-2)^x = - 1/128

solve for x

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3. 👁 64
1. does x=-7?

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posted by tom
2. yes

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posted by Steve

( - 2 )ˣ = - 1 / 128

Multiply both sides by 128

128∙( - 2 )ˣ = - 1

Raise both sides to the power 2

128²∙[ ( - 2 )² ]ˣ = ( - 1 )²

128 = 2⁷ , ( - 2 )² = ( 2 )² , so:

(2⁷)²∙(2²)ˣ = 1

_______________________________
Remark:

(2⁷)² is the same (2²)⁷
___________________________

(2²)⁷∙(2²)ˣ = 1

4⁷∙4ˣ = 1

_____________________
Remark:

nᵃ∙ nᵇ = nᵃ⁺ᵇ

Any number raised to the powe zero is one.

So:

4⁷ ∙ 4ˣ = 4⁷⁺ˣ

4⁰ = 1
_____________________

4⁷⁺ˣ = 4⁰

Take the logarithms base 4 of both sides

log₄( 4⁷⁺ˣ ) = log₄( 4⁰ )

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Remark:

log aᵐ = m ∙ log a

log₄( 4 ) = 1

So:

log₄( 4⁷⁺ˣ ) = ( 7 + x ) ∙ log₄ ( 4 ) = ( 7 + x ) ∙ 1 = 7 + x

log₄= 4⁰ = 0 ∙ log₄( 4 ) = 0
_______________________________________

7 + x = 0

Subtract 7 to both sides

7 + x - 7 = 0 - 7

x = - 7

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posted by Bosnian
4. whoa! Can you say overkill??

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posted by Steve
5. Steve

solve for x mean SOLVE for x

Just say:

x = - 7 is not enough.

I showed the way to the solution.

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posted by Bosnian

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