已知x²-3x-1=0,求代数2x³-3x²-11x+8得值!
问题描述：
已知x²-3x-1=0,求代数2x³-3x²-11x+8得值!
答
x²-3x-1=0
x²=3x+1
2x³-3x²-11x+8
=2x*x²-3x²-11x+8
=2x(3x+1)-3(3x+1)-11x+8
=6x²+2x-9x-3-11x+8
=6(3x+1) -18x+5
=18x+6-18x+5
=11
答
2x³-3x²-11x+8
=2x³-6x²-2x+3x²-9x-3+11
=2x(x²-3x-1)+3(x²-3x-1)+11
=11
答
x²-3x-1=0则：x²=3x+1原式=2x²*x-3x²-11x+8=2(3x+1)x-3x²-11x+8 把x²=3x+1代入=6x²+2x-3x²-11x+8=3x²-9x+8 再次把x²=3x+1代入=3(3x+1)-9x+8=9x+3-9x+8=11ps：方...