Bonjour,
1) 1² + (1/2)² = 1 + 1/4 = 4/4 + 1/4 = 5/4
2) 1² + (1/2)² + (1/4)² = 1 + 1/4 + 1/16 = 16/16 + 4/16 + 1/16 = 21/16
3) 1² + (1/2)² + (1/4)² + (1/8)² = 1 + 1/4 + 1/16 + 1/64
= 6464 + 16/64 + 4/64 + 1/64
= 85/64
