若m²-m-2=0则代数式m³-3m+5=

m²-m-2=0
所以：m²-m=2
m³-3m+5
=m³-m²+m²-3m+5
=m（m²-m）+m²-3m+5
=2m+m²-3m+5
=m²-m+5
=2+5
=7