解
x²-3x+4=0
x²-3x=-4
∴
x³-5x²+10x+2
=x(x²-3x)-2x²+10x+2
=x×(-4)-2x²+10x+2
=-2x²+6x+2
=-2(x²-3x)+2
=-2×(-4)+2
=8+2
=10