Math Is Fun Forum
  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

You are not logged in.

#1 2005-10-24 22:39:44

Bboy PhysicX
Guest

:: Log Functions ::

Hi! can you teach me how to do this thing?
I'm really confused... so please~~
THANK YOU~

Solve:

ln (x^2 + 1) = 2 ln (x + 1)

and

log (7x - 12) = 2 log x

#2 2005-10-24 22:57:23

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: :: Log Functions ::

Use the identity a log b = log (b^a).

1) ln (x²+1) = 2 ln (x+1)
ln (x²+1) = ln (x+1)²
x²+1 = x²+2x+1
2x = 0
x = 0

2) log (7x-12) = 2 log x
log (7x-12) = log (x²)
7x-12 = x²
x²-7x+12 = 0
(x-4)(x-3) = 0
x = 3 or 4


Why did the vector cross the road?
It wanted to be normal.

Offline

Board footer

Powered by FluxBB