3a^2+[a^2+(5a^2-2a)-3(a^2-3a)],其中a=—2.
=3a^2+[a^2+5a^2-2a-3a^2+9a]
=3a^2+3a^2+7a
=6a^2+7a
=6*(-2)^2+7*(-2)
=24-14
=10