原式=3a²b-{2ab²+

2

3

[5a³+3a²b-2a³+6a²b]}．
=3a²b-{2ab²+

10

3

a³+6a²b-

4

3

a³+4a²b}
=3a²b-2ab²-

10

3

a³-6a²b+

4

3

a³-4a²b
=-2a³-9a²b．