Question 322675
Substitute.
Let {{{u=t^3}}}, {{{u^2=t^6}}}
{{{t^6 - 18t^3 + 81=u^2 - 18u + 81}}}
{{{t^6 - 18t^3 + 81=(u-9)^2}}}
{{{t^6 - 18t^3 + 81=(t^3-9)^2}}}