Dk $x>0$
$pt<=>-log_{3}x=3x$
$<=>3^{-3x}=x$
$<=>3^{-3x}-x=0$
Nhan thay $x=\frac{1}{3}$ la mot nghiem
Xet ham $f(x)=3^{-3x}-x$
Co $f'(x)=-3.ln3.3^{-3x}-1<0 \forall x>0$
Ham so nb tren tap xac dinh nhu vay neu pt co nghiem thi nghiem do la duy nhat
Vay pt co nghiem duy nhat $x=\frac{1}{3}$