To take out terms outside the radical we need to divide the power of the term by the index of the radical; the quotient will be the power of the term outside the radical, and the remainder will be the power of the term inside the radical.
First, lets factor 8:
[tex]8=2 ^{3} [/tex]
Now we can divide the power of the term, 3, by the index of the radical 2:
[tex] \frac{3}{2} [/tex] = 1 with a remainder of 1
Next, lets do the same for our second term [tex] x^{7} [/tex]:
[tex] \frac{7}{2} [/tex] = 3 with a remainder of 1
Again, lets do the same for our third term [tex]y^{8} [/tex]:
[tex] \frac{8}{2} =4[/tex] with no remainder, so this term will come out completely.
Finally, lets take our terms out of the radical:
[tex] \sqrt{8x^{7} y^{8} }= \sqrt{ 2^{3} x^{7} y^{8} } =2 x^{3} y^{4} \sqrt{2x} [/tex]
We can conclude that the correct answer is the third one.
