Răspuns:
Explicație pas cu pas:
1/1*2 = 1/1 - 1/2
1/2*3 = 1/2 - 1/3
1/3*4 = 1/3 - 1/4
......
1/42*43 = 1/42 - 1/43
a = 1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 +...+ 1/42 - 1/43 = 1/1 - 1/43 = 43/43 - 1/43
= 42/43
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1/4*5 = 1/4 - 1/5
.......
1/125*126 = 1/125 - 1/126
b = 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + ...+ 1/125 - 1/126 = 1/2 - 1/126
= 63/126 - 1/126 = 62/126
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a/b = (42/43)/(62/126) = 42/43*126/62 = 21*126/43*31 = 2646/1333
