1.
m^2-5m+1=0,m^2=5m-1
m^4+m^2-4
=(5m-1)^2+5m-1-4
=25m^2-10m+1+5m-1-4
=25(5m-1)-5m-4
=120m-29
根据m^2-5m+1=0算出m的两个解,(5+根号21)/2和(5-根号21)/2代入,得到两个答案121+30倍的根号21,121-30倍的根号21
2.
题目错了
3.
x^2-3x+1=0,x^2=3x-1
2x^2-5x-2+3/(x^2+1)
=6x-2-5x-2+3/3x
=x-4+1/x
=(x^2-4x+1)/x
=(3x-1-4x+1)/x=-1
4.
设甲完成要x天,乙y天
则：
24*(1/x+1/y)=1
20*1/x+40*1/y=1
x=30,y=120
甲每天要a钱,乙要b钱
24(a+b)=120
20a+40b=110
a=4.5,b=0.5
故甲独自完成：4.5*30=135
乙：0.5*120=60