Re: [Math4u] MATH HELP!

Hello Jessica,
This is Raj Here.
Your 1st Question,When u have to find x in any equation the answer should be independent of x.Going by your question,ln(x+2)+ln(x-2)=ln5
Now ln(a)+ln(b)=ln(ab)
So,in the above case ln(x^2-4)=ln(5)
Removing ln,we get x^2=4+5=9,
or,x=3,since x=-3 is inadmissable.
2.ln(x-3) is not equal to lnx-ln3,rather,lnx-ln3=ln(x/3).Ok,hope this solves your Problem.
3.The third question is very simple.x^2 is always positive,and for large numbers it should >15x,which will be negative,but as we know we ca always assert a large positive number for which x^2+15x will be less.Suppose we take c=(-x)^3,which will always be larger than your term for large negative numbers.
Hope This satisfies You.
Jessica <gophert@yahoo.com> 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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