Question 610006
{{{root(13, root(7, x))}}}
It is easier to see the answer if you replace the radicals with fractional exponents. A 7th root is equivalent to an exponent of 1/7:
{{{root(13, x^(1/7))}}}
and a 13th root is equivalent to an exponent of 1/13:
{{{(x^(1/7))^(1/13)}}}
The exponent rule for a power of a power is to multiply the exponents:
{{{x^(((1/7)*(1/13)))}}}
{{{x^(1/91)}}}
Now we can revert back to radical form:
{{{root(91, x)}}}