Question 929163
this is not quite clear:
(x^3)square root of 8x^5

I assume, you have {{{(x^3)sqrt(8x^5)}}}: if yes, then

{{{(x^3)sqrt(2*2^2x^2x^2x)}}}

{{{x^3*sqrt(2)sqrt(2^2)sqrt(x^2)sqrt(x^2)sqrt(x)}}}

{{{x^3*sqrt(2)*2*x*x*sqrt(x)}}}

{{{2x^3*x^2sqrt(2)*sqrt(x)}}}

{{{2x^(3+2)sqrt(2)*sqrt(x)}}}

{{{2x^5sqrt(2)*sqrt(x)}}}



{{{sqrt((81a^2b^2)/9)}}}

={{{sqrt(9^2a^2b^2)/sqrt(3^2)}}}

={{{(cross(9)3ab)/cross(3)1}}}

={{{3ab}}}