Question 540696
You have to use the rule {{{ i^2 = -1 }}}
{{{ ( 6 + 3i )*( 6 - 3i )  = 36 + 3*6*i - 3*6*i  - 3*3*i^2 }}}
{{{ ( 6 + 3i )*( 6 - 3i )  = 36 + 18i - 18i - 9*(-1) }}}
{{{ ( 6 + 3i )*( 6 - 3i )  = 36 + 9 }}}
{{{ ( 6 + 3i )*( 6 - 3i )  = 45 }}}