e^x+e^-x=2.5 Watch

elia
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e^x+e^-x=2.5

So the way I have solved this is

e^x+1/e^-x-2.5=0
e^2x+1-2.5e^x=0

equating to y=e^x
y^2-2.5y+1=0
2y^2-5y+2=0
(2y-1)(y-2)
e^x=1/2 e^x=2

therefore x= ln0.5 or ln2

The textbook says the answer is +/-ln2.

Where did I go wrong?

Thanks
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TenOfThem
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(Original post by elia)
Where did I go wrong?

You didn't

You have the same answer
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J10
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You've got it correct. The answers are the same.
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elia
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(Original post by J10)
You've got it correct. The answers are the same.
Ah yes checked in the calculator, I always assume I'm wrong :/

Thanks guys!
/thread
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TenOfThem
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(Original post by elia)
Ah yes checked in the calculator, I always assume I'm wrong :/

Thanks guys!
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You should not need to check on the calculator

ln(1/2) = - ln(2)

Rules of logs
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Mr M
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(Original post by TenOfThem)
You should not nee to check on the calculator

ln(1/2) = - ln(2)

Rules of logs
I'd have solved the equation x = \cosh^{-1} \frac{5}{4} (she can write the answer straight down from the formula book).
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