2 Log(X) + Log 0.1 = Log 5 + Log 2

a a a a

i got X= 10 , and -10

i think all answers accepted because there is power 2 in 2 Log(X)so -10 won't be refused

is that right????

Printable View

- Jun 23rd 2012, 06:56 AMmido22log problem
2 Log(X) + Log 0.1 = Log 5 + Log 2

a a a a

i got X= 10 , and -10

i think all answers accepted because there is power 2 in 2 Log(X)so -10 won't be refused

is that right???? - Jun 23rd 2012, 07:01 AMjohnnylam123Re: log problem
2 Log(X) + Log 0.1 = Log 5 + Log 2

2logx = log (10/0.1)

2logx = log100

2logx = 2

logx=1

x=10.

x cannot be -10 ,cause logy, y<0 ,is undefined - Jun 23rd 2012, 07:03 AMjohnnylam123Re: log problem
note log is a function that have unique sol only if there is

- Jun 23rd 2012, 07:09 AMmido22Re: log problem
- Jun 23rd 2012, 07:28 AMmattoRe: log problem
x=-10 would fail the original equation.

- Jun 23rd 2012, 07:29 AMmfbRe: log problem
2Log X = Log X^2 is a formula for positive x only.

In general,

With complex numbers, you can evaluate log(-10) (it is a complex number), but you cannot use the formula given above, as -10 is not [real and] positive. - Jun 23rd 2012, 07:45 AMPlatoRe: log problem
- Jun 23rd 2012, 08:59 AMmido22Re: log problem
- Jun 23rd 2012, 09:18 AMPlatoRe: log problem
- Jun 23rd 2012, 11:12 AMjohnnylam123Re: log problem
even it is loga, results is the same