30 先化简,再求值:3a(2a²-4a+3)-2a²(3a+4),
3a(2a²-4a+3)-2a²(3a+4)
=6a³-12a²+9a-6a³-8a²
=-20a²+9a
=-20×(-2)²+9×(-2)
=-80-18
=-98