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pop000 · Jan 9, 2011, 03:53 AM

be f(x)=ln^2x-4^4x Defined for any Positive x.
how many of the sentences are correct?

1)the sum of the sqrt Equation f(x)=0 is e+1
2) the Derivative are become zero in the point: x=1/sqrt"e"
3) limf(x)=Infinity when x-->0+
4)f'(-1)=0

about 3 I think is not correct. But I need your help.
thanks.

galactus · Jan 9, 2011, 04:32 AM

Originally Posted by pop000

be $f(x)=ln^{2}(x)-4^{4x}$ Defined for any Positive x.
how many of the sentences are correct?

Do you mean the function above?

1)the sum of the sqrt Equation f(x)=0 is e+1

sum of sqrt equation?

2) the Derivative are become zero in the point: $x=\frac{1}{\sqrt{e}}$

Assuming the f(x) I have above is correct, $f'(x)=\frac{2ln(x)}{2}-8ln(2)\cdot 4^{4x}$ . Plug in $x=\frac{1}{\sqrt{e}}$ and see if you get 0 as a result.

3) $\lim_{x\to 0^{+}}f(x)=\infty$

This is obviously true. You can see it from the graph as well.

4)f'(-1)=0

If you plug x=-1 into f(x), do you get 0?

about 3 i think is not correct.

Assuming I interpreted f(x) correctly, you apear to be correct.

Which one IS correct?

thanks.

pop000 · Jan 9, 2011, 09:35 AM

no the function I mean is almost like you showed the part one as you showed with ln^2(x) is correct but the Part Two is not correct is need to be ln^4(x).

thank you.

pop000 · Jan 9, 2011, 09:36 AM

no the function I mean is almost like you showed the part one as you showed with ln^2(x) is correct but the Part Two is not correct is need to be ln^4(x).

thank you.

galactus · Jan 10, 2011, 06:57 AM

Then why did you write 4 instead of ln? You have not fixed the typo.

pop000 · Jan 10, 2011, 08:07 AM

Yes sorry is was my mistake.

galactus · Jan 10, 2011, 08:18 AM

That's OK. It will not allow you to edit now. That should be changed in the event of cases like this.