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calculati : 51 + 52 + 53 + ... + 100

Cu toate operatiile pas cu pas .


Răspuns :

Gauss 

1 + 2 + 3 + ...+ n = n(n + 1) : 2

Observam ca ne lipseste prima parte, deci vom aduna si vom scadea.

S = (1 + 2 + 3 + ... +50) + 51 + 52 + ...+ 100 - (1 + 2 + ..+ 50)

S = 100·101 : 2 - 50·51 : 2

S = 5050 - 1275

S = 3775
51 + 52 + 53 + ... + 100 =(1+2+3+4+...+51+52+53+......+99+100)-(1+2+3+...........+50)=

S1=
(1+2+3+4+...+51+52+53+......+99+100)
S2=
(1+2+3+...........+50)

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SUMA GAUSS:  S1=[(n(n+1)]/2=(100×101):2=5050
S2=[(n(n+1)]/2=(50×51):2=1275
S=S1-S2=3775