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ln(x) +ln(x+3)=1

2007-04-29 08:51:31 · 7 answers · asked by Troy 1 in Science & Mathematics Mathematics

7 answers

Use the property of the logarithms : lnA + lnB = lnAB

ln(x) +ln(x+3)=1
ln[x(x+3)]=1

Now "antilog" the equation, meaning do the:
e^(LHS) = e^(RHS)
and simplify

x(x+3) = e¹
x² + 3x - e = 0

Use the quadratic formula

x = [-3 ± √(9 + 4e)] / 2

Type this into your calculator if you want, to get
x = [-3 + √(9 + 4e)] / 2 = 0.729
and
x = [-3 - √(9 + 4e)] / 2 = -3.729
we omit the latter solution (-3.729) because log of a negative number cannot be taken.

Hope this helps.

2007-04-29 08:54:02 · answer #1 · answered by M 6 · 6 0

ln(x) + ln(x+3) = 1
ln(x+3) = 1 - ln(x)
e^(ln(x+3)) = e^(1 - ln(x))

x+3 = (e^(1))/(e^(ln(x)))

x+3 = e/x

(x+3)*x = e

x^2+3x -e =0

use quadratic equation

x = (-3+-sqr(9+4e)) / 2

x= (-3+sqr(9+4e)) / 2 only because the other one whould yeild a negative number any you cant do the natural log of a negative number

2007-04-29 16:04:47 · answer #2 · answered by Marc M 1 · 0 0

Ln[x(x+3)] = 1
x(x+3) = e
x^2 + 3x - e = 0
Solve using the genarl law
x = [-3 + sqrt ( (9 + 4e)]/2 = 0.728964295
or
x = [-3 - sqrt ( (9 + 4e)]/2 = - 3.728964295

2007-04-29 16:06:17 · answer #3 · answered by a_ebnlhaitham 6 · 0 1

ln(x) + ln(x + 3) = 1
ln[x(x - 3)] = 1
x² - 3x = e
x² - 3x - e = 0
x = [3 ± √(9 + 4e)] / 2

Since a log can't be taken of a negative number,
x = [3 + √(9 + 4e)] / 2

2007-04-29 16:03:40 · answer #4 · answered by Louise 5 · 0 0

Exponentiate both sides, to get x(x+3) = e, so x*2 + 3x - 2.718 = 0, which is solvable by the quadratic formula in the usual way.

2007-04-29 15:57:50 · answer #5 · answered by Anonymous · 0 1

ln (x.(x + 3)) = 1
x.(x + 3) = 2.718
x² + 3x - 2.718 = 0
x = [- 3 ± √(9 + 10.9)] / 2
x = [- 3 ± √(19.9)] / 2
x = 0.73 , x = - 3.73

2007-04-29 16:05:11 · answer #6 · answered by Como 7 · 0 1

Help, mI use to could do this

2007-04-29 16:07:28 · answer #7 · answered by flower wanda 3 · 0 1

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