Saturday

October 25, 2014

October 25, 2014

Posted by **Shawn** on Monday, December 1, 2008 at 2:34pm.

31.) log(x-4)+ log(x+4)= log4

I have the answer as 4

Is this answer right?

- Math help -
**bobpursley**, Monday, December 1, 2008 at 2:42pmlog a + log b is same as log ab

so log(x^2-4)=log4

taking antilogs

x^2-4=4 solve for 4

check my thinking.

- Math help -
**Shawn**, Monday, December 1, 2008 at 2:57pmOkay x^2-4 = 4

x^2= 8

sqrt(x^2)= sqrt 8

x= 2.83 is this right?

- Math help -
**Reiny**, Monday, December 1, 2008 at 3:04pmlog k has a nasty habit of becoming undefined if k is not positive.

you answer of x = 2.832 is correct according to the steps taken, but...

when we sub into log (x-4) we get log (-1.168 which is undefined,

so there is no solution in the set of real numbers for your equation

- Correction: Math help -
**Reiny**, Monday, December 1, 2008 at 3:21pmGoing back and looking over the previous solutions, I noticed that the original non-log equation should have said:

x^2-16 = 4

so x^2 = 20

x = √20 = 4.472136

which works upon substituting.

- Correction: Math help -

**Answer this Question**

**Related Questions**

Algebra help 2 - Where appropriate, include the approximation to the nearest ten...

Algebra check - Where appropriate, include the approximation to the nearest ten-...

algebra - find an approximation to the nearest ten-thousandth log 8900 over log ...

Algebra - what would be the approximation to the nearest ten-thousandth log 8900...

math - Logarithm!!! Select all of the following that are true statements: (a) ...

Algebra - Where appropriate, include the approximation to the nearest ten-...

calculus - Use a linear approximation of f(x)=log(x) at x=1 to approximate log(3...

algebra - Solve. Where appropriate, include approximations to the nearest ...

college algebra - Write expression as one logarithm and simplify if appropriate...

Math Help Please - Which of the following expressions is equal to log (x sqrt-y...