当a=-3/2时,求代数式15a^2-{-4a^2+[5a-8a^2-(2a^2-a)+9a^2]-3a}

15a^2-{-4a^2+[5a-8a^2-(2a^2-a)+9a^2]-3a}
=15a^2-{-4a^2+[5a-8a^2-2a^2+a+9a^2]-3a}
=15a^2-{-4a^2+[6a-a^2]-3a}
=15a^2-{-4a^2+6a-a^2-3a}
=15a^2-{-5a^2+3a}
=15a^2+5a^2-3a
=20a^2-3a
=20×（-3/2）²-3×(-3/2)
=20×9/4+9/2
=45+9/2
=99/2

数学符号不好打，给你说下思路吧，这种题，一般都是先化简，然后带入

原代数式可化为
15a^2+4a^2-5a+8a^2+2a^2-a-9a^2+3a
=20a^2-3a
=a(20a-3)
将 a=-3/2代入
有 (-3/2)[20*(-3/2)-3]
=(-3/2)*(-33)
=99/2