已知代数式2a²-3b+5的值为8;求6b-7-4a²的值

已知代数式2a²-3b+5的值为8;求6b-7-4a²的值
已知代数式2a²-3b+5的值为8;求6b-7-4a²的值

已知代数式2a²-3b+5的值为8;求6b-7-4a²的值
2a²-3b+5的值为8
2a²-3b=3
6b-7-4a²
=-2（a²-3b)-7
=-2×3-7
=-13

2a²-3b+5=8 ==>2a²-3b=3 ==>4a²-6b=6 ==>-4a²+6b=-6 ===> 6b-7-4a²=-13