x的平方-3x=1
即
x²-3x=1
3x的三次方-11x的平方+3x+2
=3x³-11x²+3x+2
=3x³-9x²-2x²+3x+2
=3x(x²-3x)-2x²+3x+2
=3x-2x²+3x+2
=-2x²+6x+2
=-2(x²-3x)+2
=-2+2
=0