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Posted by **Sara** on Sunday, January 15, 2012 at 1:19pm.

e^x-42e^-x= -19

- precalculus -
**Reiny**, Sunday, January 15, 2012 at 4:39pmmultiply each term by e^x

(e^x)^2 - 42 + 19e^x = 0

let y = e^x

y^2 + 19y - 42 = 0

(y+21)(y-2) = 0

y = -21 or y = 2

so e^x = 2

x = ln 2

or

e^x = -21, which has no solution

x = ln2

- precalculus -
**Sara**, Sunday, January 15, 2012 at 5:46pmthanks again

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