# Thread: Logarithme Help

1. ## Logarithme Help

Hello Guys i have a logarithme lesson, and our teacher gave us some exercices but he didn't explain all the lesson.

compare without a calculater:
Ln7 and ln2 + ln 3
For me: 7>3+5 --> Ln7>ln5

3+ln (radical)e and 4 ? well i don't know how to compare it.

Resolve this:
lnx =1 ; ln 2x=0 ; lnx=-1 ; lnx=3 ( what i have to do here)??

ln(x-3)=ln(x+7)-ln(x+1)??
ln(x^2-2x-3) = ln(x+7)

the teacher told us to do them and he gave us this
ln(ab) = ln (a) +ln(b) but i can't do them....
Please help me i have many exercices like these and when somebody could help me i guess i can solve the others ones

Many thanks in advance

2. Originally Posted by iceman1
Ln7 and ln2 + ln 3
$\ln 2+\ln 3=\ln 6<\ln 7$

3+ln (radical)e and 4
$3+\ln\sqrt{e}=3+\frac{1}{2}\ln e=3+\frac{1}{2}<4$

Resolve this:
lnx =1 ; ln 2x=0 ; lnx=-1 ; lnx=3
Here you can use this: $\log_ab=c\Leftrightarrow b=a^c$

ln(x-3)=ln(x+7)-ln(x+1)
$\ln(x-3)=\ln(x+7)-\ln(x+1)\Leftrightarrow\ln(x-3)+\ln(x+1)=\ln(x+7)\Leftrightarrow$
$\Leftrightarrow\ln(x-3)(x+1)=\ln(x+7)\Leftrightarrow(x-3)(x+1)=x+7$
Now you can continue.

3. Oh Thanks , I'll try to solve them all Now

4. i solved this:
Ln(2+ radical 3)^30 + Ln(2+radical 3)^3 my result is 0
(x+2)Ln(x+2) i got x = -1

But i need Help with this Guys

Ln(x^2 - 4)=Ln5 + 2Ln3
Ln(Radical) 3-x + Ln(radical)x+1=Ln(radical)10-6x --> should i make them ^2?

system:
x+y=30
Lnx +lny=3Ln6

i did the resr but one question how to find the derivebality of this
Ln=[1-x^2]

p.s For the Last question [ ] = sorry about the ''z'' LOL it's Nothing

Thanks Now i am starting to love math and my teacher told my mum that i am contribution at class