find the domain of f(x)=ln(7x-42)

Question

anonymous · Answer

7x-42 has to be > 0 because the ln function is not defined for x <= 0.  So, just solve the inequality 7x-42 > 0.

anonymous · Answer

Thank for the confirmation can you help with 1 more?

anonymous · Answer

I f I can.

anonymous · Answer

find the domain of f(x)=ln(5x)

anonymous · Answer

|dw:1348870559160:dw| Well, that's similar.  I'm going to get you to think through this, because you should or you won't understand exponents and logs.  The ln x function is asking for the exponent one has to put on e (which is a positive number) to get x.  You can never put any exponent on e and get a negative number.  Think of the graph.  So, lookingat the graph, what can you say about the ln function?

anonymous · Answer

that it's positive and increasing

anonymous · Answer

Yes, very good.  It also helps to think visually about logs and exponents with each being the inverse of the other.  Look at inverse graphs.|dw:1348870815490:dw|