Question 401370
 ^4 over the square root of (9a)^4 
IF YOU MEAN  {{{root(4,(9a)^4)}}}
use formula {{{root(n,x^n)=abs(x)}}} if n is even
_________{{{root(n,x^n)=x}}} if n is odd
{{{root(4,(9a)^4)=abs(9a)=9abs(a)}}}
OR YOU MEAN {{{(sqrt((9a)^4))^4=((9a)^2)^4=(9a)^(2*4)=(9a)^8}}} 
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Used formulas {{{root(n,x)=x^(1/n)}}} (so {{{sqrtx=x^(1/2)}}}), {{{(x^k)^m=x^(k+m)}}}
so {{{sqrt((9a)^4)=((9a)^4)^(1/2)=(9a)^(4*(1/2))=(9a)^2}}}