Răspunsuri

2014-01-31T09:29:14+02:00
Observam ca:
9=2³+1³ (=8+1=9)
35= 3³+2³ (=27+8=35)
91= 4³ + 3³ (= 64 +27=91)
189= 5³+4³ (=125+64=189)

De unde deducem ca sirul este an=n³+(n+1)³
(an=2n³-3n²+3n-1)
2014-01-31T19:17:35+02:00
R:
9=2³+1³ (=8+1=9)
35= 3³+2³ (=27+8=35)
91= 4³ + 3³ (= 64 +27=91)
189= 5³+4³ (=125+64=189