# Logarithm Equation Question 2 [Checking validity of answers in logarithms equations]

Solve the equation

$\lg(3a+2)+ lg(5a-3)=1+ 2lg (a)$

Ans : a = 1 or -6/5

Question : Do we need to include -6/5

Contributed by YC

It is important for you to check if your answers are valid i.e are there any answers you would need to reject?
This is what I called checking for validity of answers.

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### 5 Responses to Logarithm Equation Question 2 [Checking validity of answers in logarithms equations]

1. Humairah says:

I guess, we do not include -6/5 as there is no such graph of log(-a).

Reply

2. Algebra says:

Clearly the domain (admissible values of x for the argument of the function f(x)=lg(x)) of f(x) is (0, \infty). If a=-6/5, then 3a+2 is negative; therefore x=-6/5 is not admissible into the domain of function f(x).

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