Solve log2(x) - log3(4x-5) > 1
that's base 2 and base 3.
I tried using change of base w/ ln and then multiplying by ln2ln3 but I'm not sure where to go from there.
ln(3)ln(x) - ln(2)ln(4x-5) > ln(2)ln(3) and then? Or is there another way.
2 Answers | Add Yours
After playing with this for a while I do not see anyway to solve for x.
If you are in a Calculus class there is a way to approximate this root using Newton's Method.
I graphed y=log_2(x) - log_3(4x-5) - 1 and zeroed in on where this crossed the x axis. I get x `~~` 1.395243. So log_2(x) - log_3(4x-5) > 1 when x < 1.3905243
First, you need to create matching bases to both logarithms:
log a (x) = log b (x)/log b (a)
log3(x) = log2(x)/log2 (3) => log2(x) = log3(x)*log2 (3)
The inequality will become:
log3(x)*log2 (3) - log3(4x-5)
But log2 (3) = lg3/lg2 = 0.4771/0.3010=1.585
1.585log3(x) - log3(4x-5) > 1
log3 (x^1.585) - log3(4x-5) > 1
Since the bases are matching, we'll use quotient rule:
log3 (x^1.585/(4x-5)) > 1
We'll write 1 as log3 (3)
x^1.585/(4x-5) > 3
(x^1.585 - 12x + 15)/(4x-5) > 0
Both numerator and denominator must be positive or negative, to keep the fraction positive.
The denominator is positive for x>5/4
We’ve answered 319,865 questions. We can answer yours, too.Ask a question