已知x=2,多项式-ax3-[8-(bx+2ax3)]的值为5.求当x=-2时代数式的值.

问题描述:

已知x=2,多项式-ax3-[8-(bx+2ax3)]的值为5.求当x=-2时代数式的值.

当x=2时,
-ax3-[8-(bx+2ax3)]
=-8a-[8-(2b+16a)]
=-8a-8+2b+16a
=8a+2b-8=5
8a+2b=13;
当x=2时,
-ax3-[8-(bx+2ax3)]
=8a-[8-(-2b-16a)]
=8a-8-2b-16a
=-(8a+2b)-8
=-13-8
=-21.