Răspuns:
Explicație pas cu pas:
2/1×3 = 1 - 1/3
2/3×5 = 1/3 - 1/5
.............
2/49×51 = 1/49 - 1/51
___________
2/1×3 + 2/3×5 +...+ 2/49×51 = 1 - 1/3 + 1/3 - 1/5 + ... + 1/49 - 1/51
a = 1 - 1/51 = 51/51 - 1/51 = 50/51
1/2 < 50/51 < 1
51/102 < 100/102 < 102/102 adevarat