化简（as-3t)²-（4s+3t）²

化简（as-3t)²-（4s+3t）²

a应该是4吧,你可能抄错题了.
(4s-3t)²-(4s+3t)²
=[(4s-3t)+(4s+3t)][(4s-3t)-(4s+3t)]
=8s·(-6t)
=-48st

（as-3t)²-（4s+3t）²
=(as)²+(3t)²-6ats-[(4s)²+(3t)²+24ts]
=a²s²+9t²-6ats-16s²-9t²-24ts
=a²s²-6ats-16s²-24ts

=a²s²-6ast+9t²-16s²-24st-9t²
=a²s²-6ast-16s²-24st