Question

x²-3x=1=0求代数式2x³-3x²-11x+8

A=2x²=3xy-2x-1 B=-x²+xy-1，且3A+6B的值与x无关，求y的值

Answer 1

2x³-3x²-11x+8
=2x³-6x²+3x²-9x-2x+8
=2x(x²-3x)+3(x²-3x)-2x+8
假如x²-3x=1
=2x+3-2x+8
=11
假如x²-3x=0
=-2x+8

Answer 2

解：2x³-3x²-11x+8
=2x（x²-3x-1）+3(x²-3x-1)+11
=11

Answer 3

x²－3x=1 ===>>> x²=3x＋1
2x³－3x²－11x＋8
=2x(3x＋1)－3(3x＋1)－11x＋8 ====>>>>> x²=3x＋1
=6x²－18x－1
=6(x²－3x)－1 ======>>>> x²－3x=1
=5

Answer 4

2x³-3x²-11x+8
=2x（x²-3x-1）+3(x²-3x-1)+11
=11