Question

lg²x³-10lg x +1= 0. x=?

Answer 1

Consideram lg x=t
lg x^3=3*lg x
Ecuatia va fi: 3t^2-10t+1=0.
Calculam Δ=10^2-4*3*1=100-12=88 =>√Δ=2√22
t(1)=(10+2√22)/2=5+√22
t(2)=(10-2√22)/2=5-√22
lg x1=5+√22
lg x2=5-√22
x1=e^(5+√22)
x2=e^(5-√22)