How do you solve log_3(x+6)-log_9x=log_9 2?

1 Answer
Nov 2, 2016

x = O/

Explanation:

Use the change of base formula, log_a(n) = logn/loga, to start the solving process.

log(x + 6)/log3 - logx/log9 = log2/log9

log(x + 6)/log3 - logx/log3^2= log2/log3^2

log(x + 6)/log3 - logx/(2log3) = log2/(2log3)

Put on a common denominator.

(2log(x + 6))/(2log3) - logx/(2log3) = log2/(2log3)

log_9(x + 6)^2 - log_9x = log_9 2

We now use the property log_a(n) - log_a(m) = log_a(n/m) to solve.

log_9((x + 6)^2/x) = log_9 2

(x^2 + 12x + 36)/x = 2

x^2 + 12x + 36 = 2x

x^2 + 10x + 36 = 0

x = (-b +- sqrt(b^2 -4ac))/(2a)

x = (-10 +- sqrt(10^2 - (4 xx 1 xx 36)))/(2(1))

x = (-10 +- sqrt(-44))/2

x = (-10 +- 2sqrt(11)i)/2

x = -5 +- sqrt(11)i

This does not satisfy the original equation, and hence there are no solutions.

Hopefully this helps!