Thread: Logarithmic problem help

I have to solve x in terms of k

log(x) + log(y) = log(xy)

Originally Posted by Also sprach Zarathustra

log(x) + log(y) = log(xy)

Sorry wrote that completely wrong, meant to say solve for X in terms of K

Yes, Also Sprach Zarathustra understood that. Apply his hint. If "log(x)+ log(y)= log(xy)" is a general rule, then what is log(x)+ log(x+ 9)?

Do you know how to solve log(y)= k for y? Do you know what the inverse function to log(x) is?

Originally Posted by HallsofIvy

Yes, Also Sprach Zarathustra understood that. Apply his hint. If "log(x)+ log(y)= log(xy)" is a general rule, then what is log(x)+ log(x+ 9)?

Do you know how to solve log(y)= k for y? Do you know what the inverse function to log(x) is?

I haven't taken pre calc in 3 years so my memory of it is really sketchy..this is a review problem for calc which I'm taking right now.

Log(x^2+9x)=k
10^k=(x^2+9x)

Can't really figure out where to go from there. Like I said I barely remember anything from pre calc since its been about 3 years.

That's the right way to do it, now notice that it is equal to the equation , which is a quadratic equation in with a constant term in . Therefore you can apply the quadratic formula to isolate and solve it in terms of .