✔ 最佳答案
Split the 9 into 3 * 3:
(3*3)^log_3(log x) = log(x) - 2 log²(x) + 4
Use this rule --> (a*b)^c = a^c * b^c:
3^log_3(log x) * 3^log_3(log x) = log(x) - 2 log²(x) + 4
Simplify the two logs on the left:
log(x) * log(x) = log(x) - 2 log²(x) + 4
log²(x) = log(x) - 2 log²(x) + 4
Get everything on the left hand side:
3 log²(x) - log(x) - 4 = 0
Use this substitution --> u = log(x)
3u² - u - 4 = 0
Factor:
(u + 1)(3u - 4) = 0
Find the two possible values:
u = -1
or
u = 4/3
Substitute back in for u:
log(x) = -1
or
log(x) = 4/3
But we can't take log_3 of a negative number, so we can drop the negative answer.
Next, I'm not sure if you are using 'log' to mean the common log (base 10) or the natural log (base e).
Assuming the common log, raise both sides upon the base 10:
x = 10^(4/3)
x ≈ 21.5443469...
(If it is the natural log, then x = e^(4/3) ≈ 3.79366789...)