Question

find the solution for the logarithmic equation
ln(x+8) +ln(x-8)=0

Answer 1

x=-7 and x=9

Answer 2

(x+8)(x-8)=1
Solve th quadratic

Answer 3

-7 is not a valid solution

Answer 4

x=9

Answer 5

Log(x-8)=0

Answer 6

x=-7

Answer 7

you cannot define logarithm for a negative number

Answer 8

You can

Answer 9

i dont think she knows complex logarithms

Answer 10

yes you can say log (17e^(i*pi)) .....but thats not what she might want

Answer 11

http://www.wolframalpha.com/input/?i=ln%28x%2B8%29+%2Bln%28x-8%29%3D0
This is how I would look at this one. :)

Answer 12

It can be negative

Answer 13

x=-7

Answer 14

Look it up if ya like.

Answer 15

wolfram shows were both fools....root65 is the answer

Answer 16

i told you i know there can be negative logarithms...they just dont need em at this level...there are even logs of quantities that are sums of scalars and vectors..would you want to know that before your exam?

Answer 17

i don't get it, can someone show their work?

Answer 18

ln(x+8) +ln(x-8)=0
ln a + lnb = ln(a.b)
(a +b) ( a - b) = a^2 - b^2
(x+8) (x-8) = ( x^2 - 8^2)
-> ln (x^2 - 64) = 0
Exponent both side by e:
=> x^2 - 64 = e^0 = 1
=> x^2 = 64 + 1 = 65
Thus x = +/- sqrt (65) = 8.06, -8.06