Question

请教数学题目

已知x²-3x=1,求代数式2x³-3x²-11x+8的值

Answer 1

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

Answer 2

因为x²-3x-1=0
所以x²-3x
=12x³-3x²-11x+8
=2x³-6x²+3x²-11x+8
=2x(x²-3x)+3x²-11x+8
=2x+3x²-11x+8
=3x²-9x+8
=3(x²-3x)+8
=3+8
=11