Homework Help: precalculus

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

solve exponential equation. express in exact form.
e^x-42e^-x= -19

precalculus - Reiny, Sunday, January 15, 2012 at 4:39pm
multiply 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 5:46pm
thanks again

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