Answer
$7y^{2}\sqrt y$
Work Step by Step
$\frac{\sqrt (98y^{6})}{\sqrt (2y)}=\sqrt \frac{98y^{6}}{2y}=\sqrt (49y^{5})=\sqrt (49\times y^{4}\times y)=\sqrt 49\times \sqrt(y^{4})\times \sqrt(y)=7y^{2}\sqrt y$
We know that $\sqrt 49=7$, because $7^{2}=49$.
We know that $\sqrt (y^{4})=y^{2}$, because $(y^{2})^{2}=y^{2\times2}=y^{4}$
