How do you solve log (x + 8) = 1 + log (x - 10)log(x+8)=1+log(x10)?

1 Answer
Dec 14, 2015

x = 12x=12

Explanation:

Begin by moving both of the loglog terms to the left hand side.

log(x+8) - log(x-10) = 1log(x+8)log(x10)=1

Now we can use the division rule for logarithms to combine both terms into one. The division rule states that;

log(m/n) = log(m) - log(n)log(mn)=log(m)log(n)

Letting m=x+8m=x+8 and n=x-10n=x10, we get;

log((x+8)/(x-10)) = 1log(x+8x10)=1

Since we are working with a common loglog it is base ten. That means that the part inside of the parenthesis is equal to 1010 raised to the power of the right hand side, or;

10^1 = (x+8)/(x-10)101=x+8x10

Now we just need to do some algebra to solve for xx. First, multiply both sides by (x-10)(x10).

10(x-10) = x+810(x10)=x+8

Now multiply the 1010 through the parenthesis.

10x - 100 = x + 810x100=x+8

Subtract xx and add 100100 to both sides.

9x = 1089x=108

Finally, divide both sides by 99 to find xx.

x = 12x=12