计算机结果分数改小数点,程序中分数结果怎样才能变成小数的结果？

Phi =

(a/4 + 5/4)^2 + ((7*a)/16 - 3/4)^4 + (a/4 + 5/4)*((7*a)/16 - 3/4)

diff_phi =

(11*a)/32 + (7*((7*a)/16 - 3/4)^3)/4 + 63/64

diff2_phi =

(147*((7*a)/16 - 3/4)^2)/64 + 11/32

a =                                                                                                                                                                                            ((373714754427^(1/2)*10952173600768^(1/2))/373714754427 - 90240/16807)^(1/3) - 5632/(7203*((373714754427^(1/2)*10952173600768^(1/2))/373714754427 - 90240/16807)^(1/3)) + 12/7

2816/(7203*((373714754427^(1/2)*10952173600768^(1/2))/373714754427 - 90240/16807)^(1/3)) - ((373714754427^(1/2)*10952173600768^(1/2))/373714754427 - 90240/16807)^(1/3)/2 + 12/7 - (3^(1/2)*(5632/(7203*((373714754427^(1/2)*10952173600768^(1/2))/373714754427 - 90240/16807)^(1/3)) + ((373714754427^(1/2)*10952173600768^(1/2))/373714754427 - 90240/16807)^(1/3))*i)/2

2816/(7203*((373714754427^(1/2)*10952173600768^(1/2))/373714754427 - 90240/16807)^(1/3)) - ((373714754427^(1/2)*10952173600768^(1/2))/373714754427 - 90240/16807)^(1/3)/2 + 12/7 + (3^(1/2)*(5632/(7203*((373714754427^(1/2)*10952173600768^(1/2))/373714754427 - 90240/16807)^(1/3)) + ((373714754427^(1/2)*10952173600768^(1/2))/373714754427 - 90240/16807)^(1/3))*i)/2