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September 18, 2014

September 18, 2014

Posted by **tina** on Friday, November 11, 2011 at 12:40pm.

18e^-x -e^x=7

- precalculus -
**Reiny**, Friday, November 11, 2011 at 12:47pm18/e^x - e^x = 7

let e^x = a

18/a - a - 7 = 0

18 - a^2 - 7a = 0

a^2 + 7a - 18 = 0

(a+9)(a-2) = 0

a = -9 or a = 2

then

e^x = -9 ----> no solution

or

e^x = 2

x = ln 2

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