Persamaan kuadrat, yg akar²nya 3 dan 2/5 adalah

x1 + x2 = 3 + 2/5 = 15/5 + 2/5 = 17/5

x1 . x2 = 3 × 2/5 = 6/5

Pers. kuadrat:
x^2 - (x1 + x2)x + (x1 . x2) = 0
x^2 - 17/5 x + 6/5 = 0
------------------------- (kali 5)
5x^2 - 17x + 6 = 0