Question

se da exercitiul 1+3+5+....+53

Answer 1

S = 1 + 3 + 5 + ... + 49 + 51 + 53 (27 de termeni)
S = 53 + 51 + 49 + ... + 5 + 3 + 1 (27 de termeni)
2 x S= 54 + 54 + 54 + ... + 54 + 54 + 54 (27 de termeni)
2 x S = 27 x 54
2 x S = 1458
S = 1458 : 2
S = 729

Answer 2

pas=2 (numerele sunt din 2 in 2). 1=2*1-1. 2=2*2-1. 3=2*3-1.... 53=2*27-1. S=2*1+2*2+2*3+...+2*27-27. S=2(1+2+3+...+27)-27. S=2*27*28supra2-27. S=27*28-27. S=27(28-1). S=729