先化简再求值：5x²-[3x-2(2x-3)-4x²],其中x=-1/2

5x²-[3x-2(2x-3)-4x²]
=5x²-（3x-4x+6-4x²）
=5x²+x-6+4x²
=9x²+x-6
x=-1/2
9x²+x-6
=9*1/4-1/2-6
=-17/4

5x²-[3x-2(2x-3)-4x²]，
=5x²-3x+4x-6+4x²
=9x²+x-6
=9/4-1/2-6
=-17/4

先化简再求值：5x²-[3x-2(2x-3)-4x²]，其中x=-1/2
=5x²-3x+2(2x-3)+4x²
= 5x²+4x²-3x+4x-6
=9x²+x-6 当x=-1/2时
原式=-8.75

5x²-[3x-2(2x-3)-4x²]=5x²-(6-x-4x²)=9x²+x-6
将x=-1/2代入得9*1/4-1/2-6=-17/4

5x²-[3x-2(2x-3)-4x²]
=5x²-[3x-4x+6-4x²]
=5x²-[-x+6-4x²]
=5x²+x-6+4x²
=5x²+4x²+x-6
=9x²+x-6
=9*(-1/2)²-1/2-6
=9/4-1/2-6
=9/4-2/4-24/4
=(9-2-24)/4
=-17/4