`log_3(x) + log_3(x - 2) = 1`
The logarithms at the left side have the same base. So express the left side with one logarithm only using the rule `log_b (M) + log_b (N) = log_b(M*N` ).
`log_3(x * (x-2)) = 1`
`log_3 (x^2 - 2x) = 1`
Then, convert this to exponential form.
Take note that if a logarithmic equation is in the form
`y = log_b (x)`
its equivalent exponential equation is
`x = b^y`
So converting
`log_3 (x^2 - 2x) =1`
to exponential equation, it becomes:
`x^2-2x = 3^1`
`x^2 - 2x = 3`
Now the equation is in quadratic form. To solve it, one side should be zero.
`x^2 - 2x - 3 = 0`
Factor the left side.
`(x - 3)(x +1)=0`
Set each factor equal to zero. And isolate the x.
`x - 3 = 0`
`x=3`
`x + 1=0`
`x = -1`
Now that the values of x are known, consider the condition in a logarithm. The argument of a logarithm should always be positive.
In the equation
`log_3(x) + log_3(x - 2)=1`
the arguments are x and x - 2. So the values of these two should all be above zero.
`x gt 0`
`x - 2gt0`
Between the two values of x that we got, it is only x = 3 that satisfy this condition.
Therefore, the solution is `x=2` .
No comments:
Post a Comment