3a+(-8a+2)-(3-4a)
=3a-8a+2-3+4a
=-a-1
4a^2b-[3ab^2-2(3a^2b+ab^2)]
=4a^2b-3ab^2+6a^2b+2ab^2
=10a^2b-ab^2
3(2a+3b)-2(-3a+4b)+5(2a+4b),其中a=3/11,b=-1/21
3(2a+3b)-2(-3a+4b)+5(2a+4b)
=6a+9b+6a-8b+10a+20b
=22a+21b
当a=3/11,b=-1/21时
原式=22×3/11+21×(-1/21)
=6-1
=5
9a^3-[-6a^2+2(a^3-2/3a^2)].其中a=-2
9a^3-[-6a^2+2(a^3-2/3a^2)]
=9a^3+6a^2-2a^3+4/3a^2
=7a^3+22/3a^2
当a=-2时
原式=7×(-2)^3+22/3×(-2)^2
=-56+88/3
=-80/3