化简求值数学题!先化简,再求值:(3a²-8a)+(2a³-13a²+2a)-2(a³-3),其中a=-2(3a²-ab+7)-(5ab+4a²-7),其中a=-2,b=三分之一

1.
(3a²-8a)+(2a³-13a²+2a)-2(a³-3)
= 3a^2-8a+2a^3-13a^2+2a-2a^3+6
= -10a^2-6a+6
将a=-2带入
-10a^2-6a+6
= -10*（-2）^2-6*(-2)+6
= -10*4+12+6
= -22
2.
（3a²-ab+7)-(5ab+4a²-7)
=3a^2-ab+7-5ab-4a^2+7
=-a^2-6ab+14
将a=-2，b=1/3带入
-a^2-6ab+14
=-（-2)^2-6*(-2)*(1/3)+14
=-4+4+14
=14

(3a²-8a)+(2a³-13a²+2a)-2(a³-3)
=3a²-8a+2a³-13a²+2a-2a³+6
=6-6a²-10a
=6-6*2²-10*2
=-38
(3a²-ab+7)-(5ab+4a²-7)
=3a²-ab+7-5ab-4a²+7
=14-6ab-a²
=14-6*2*1/3-2²
=6

:(3a²-8a)+(2a³-13a²+2a)-2(a³-3),
=3a²-8a+2a³-13a²+2a-2a³+6
=-10a²+6a+6
当a=-2时
原式=-40-12+6
=-46
(3a²-ab+7)-(5ab+4a²-7)
=3a²-ab+7-5ab-4a²+7
=-a²-6ab+14
当a=-2,b=三分之一时
原式=-4+4+14
=14