Question 535379
{{{ sqrt(-81) * sqrt(-36) }}}
Note that {{{ sqrt(-1) = i }}}
{{{ sqrt(81)*sqrt(-1)*sqrt(36)*sqrt(-1) }}}
{{{ sqrt(81)*i*sqrt(36)*i }}}
{{{ sqrt(81)*sqrt(36)*i^2 }}}
note that {{{ i^2 = -1 }}}
{{{ 9*6*(-1) }}}
{{{ -54 }}}
Note also that square roots can be + or -,
so the answer is
{{{ 54 }}} and {{{ -54 }}}