已知x=2时,代数式 -ax^3-[7-(bx+2ax^3)]的值为5
-ax^3-[7-(bx+2ax^3)]=5
-ax^3-7+(bx+2ax^3)=5
-ax^3-7+bx+2ax^3=5
ax^3+bx=12
a*2^3+2b=12
8a+2b=12
4a+b=6
x=-2
-ax^3-[7-(bx+2ax^3)]
=-ax^3-7+bx+2ax^3
=ax^3-7+bx
=a*(-2)^3-7-2b
=-8a-2b-7
=-2(4a+b)-7
=-2*6-7
=-19