Answer
$x=a^6$
Work Step by Step
$\sqrt{x}-a\sqrt[3]{x}+b\sqrt[6]{x}-ab=0$
$\sqrt[6]{x}^3-a\sqrt[6]{x}^2+b\sqrt[6]{x}-ab=0$ (Factorize)
$(\sqrt[6]{x}-a)(\sqrt[6]{x}^2+b)=0$ (Note that $\sqrt[6]{x}^2+b>0$)
$\sqrt[6]{x}-a=0$
$\sqrt[6]{x}=a$
$x=a^6$
Then, the solution is $x=a^6$.