Răspuns:
(5/3)⁴ : 25⁶ - 1 = 625/81+1/25⁶ - 1 = 25²/81×1/25⁶ - 1 => simplificam cu 25² ->
1/81×1/25⁴-1=1/81×25⁴-1 ≈ -1