[Math4u] Re: MATH HELP!

I don't know who teaches you math but the idea from #2 is completely
incorrect. You should refer to your natural log rules and know that
ln (x) + ln(y) = ln (xy). Also, #1 has a unique solution of x=3. To
prove this:

ln(x-2)+ln(x+2) = ln5
ln((x-2)(x+2))=ln5 (exponentiate both sides)
(x-2)(x+2)=5
x^2 - 4 = 5
x^2 - 9 = 0
x = +3,-3
But X=-3 is not a solution for the original equation
Therfore x=3.
As far as #3, that is always possible seeing that the set of positive
integers is infinate.
--- In Math4u@yahoogroups.com, "Jessica" <gophert@...> wrote:
>
> Can someone help me solve these three problems?
>
>
> #1 Suppose ln(x+2)+ln(x-2)=ln(5) and the question is : "Find `x'".
Is
> the answer a number (and if so what number) or some expression
> involving x?
>
> #2 Suppose ln (x-3)=ln(x)-ln(3) {for all x}. Then it would be true
> that ln22=ln25-ln3. But ln22=3.09; ln25=3.22;ln3=1.1 [YOU can use a
> calculator!!]. But, 3.22-1.1=2.12 NOT 3.09. What is wrong!. You must
> never forget the Barber who shaves all men and only those men who do
> not shave themselves. And since we know there is no such Barber,
what
> does that say about ln(x+y)=lnx+lny?
>
> #3 If x is a large negative number (e.g. –1000, -1000000000, your
> call) is it possible that x^2+15x<c, where "c" is any positive
> integer? Why or why not?
>

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