Question 273074
The general rules for powers raised to powers are:
(1) {{{(a^b)^c = a^(b*c)}}}
(2) {{{(a^(-b))^c = a^(-b*c)}}}
(3) {{{(a^b)^(-c) = a^(b*(-c))}}}
(4) {{{(a^(-b))^(-c) = a^((-b)*(-c))}}}
The other rules you need are
(5) {{{1/(a^b) = a^(-b)}}}
(6) {{{1/(a^(-b)) = a^b}}}
Notice that (1) and (4) give the same result, and
(2) and (3) give the same result
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{{{(u^4)^(-7) = 1/(u^4)^7}}} (this is just rule (5) backwards)
{{{(u^4)^(-7) = (1/u^4)*(1/u^4)*(1/u^4)*(1/u^4)*(1/u^4)*(1/u^4)*(1/u^4)}}}
{{{(u^4)^(-7) = 1/u^(4+4+4+4+4+4+4)}}}
{{{(u^4)^(-7) = 1/u^28}}}
{{{(u^4)^(-7) = u^(-28)}}}
This is just rule (3)