Question

va rogue mult sa ma ajutati! ​

Answer 1

Răspuns:

Explicație pas cu pas:

a)

1/1*2 = 1/1 - 1/2

1/2*3 = 1/2 - 1/3

1/3*4 = 1/3 - 1/4

............

1/99*100 = 1/99 - 1/100

_____________

1/1*2 + 1/2*3 + 1/3*4 + ... + 1/99*100 = 1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/99 - 1/100 = 1/1 - 1/100 = 100/100 - 1/100 = 99/100

x*99/100 = 99 ⇒ x = 99 : 99/100 = 99*100/99 = 100

b)

1 + 2 + 3 + .. + 50 = 50*51/2 = 25*51

1/1*2 + 1/2*3 + 1/3*4 + ... + 1/25*26 = 1 - 1/26 = 25/26 (aplici acelasi model de calcul ca la punctul a)

1/51*x*25*51 = 25/26

x*25 = 25/26

x = 25/26 : 25 = 1/26