log(x) + log(2x) = log(18)
In the beginning, you can't find the antilog of both sides because the left side isn't just one log. But, you can turn the addition of two logs into one log by combining them this way:
log(x · 2x) = log(18)
log(2x²) = log(18)
Once you have the equation so that both sides are logs, find the antillog of both sides:
2x² = 18
x² = 9
Either x = 3 <--- answer!
or x = -3 <--- impossible because the log of a negative number, such as log(-3), is undefined
