inverse function of F(x) = e^x + e^2x ??? (1 Viewer)

[Li0n]

Topic ^^

was in JR ext-1 trial 04 paper if your wondering

 

[ae]

swap x&y
so, x=e^2y+e^y
then, (e^y)^2 +e^y - x = 0
then use quadractic formula.
e^y= ......

then y= ln.....

 

[Archman]

ye, just keep in mind that e^y is positive.

 

[Li0n]

thanks homie
^_^

 

[Iota]

f(x)=e^x+e^2x
ln(f(x))=x+2x=3x, divide by 3 and interchange f(x) and x
(1/3)lnx=f^-1(x)

So why did I get it wrong?

 

[Estel]

When you take the ln of the LHS you have to do it to the whole of the LHS, not just individual terms.

i.e. x + y = z then (x+y)^2 = z^2 not x^2 + y^2 = z^2

 

[Iota]

Ah. I forgot about that. Silly me.

 

[ngai]

ahh, that question...haha