Question

CALculati :
a) S=1+2+3+.......+57

b) S=3+4+5+......+26

c) S=1+2+3+......100

d) S=13+14+15+.........+88

va rog repede
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Answer 1

Răspuns:

1. Sirul Gauss: 1+2+3+4+...57 =(1+57)/2*57 = 29*57

2. 2+3+4+5+...26=1+2+3+...26 -1-2= (1+26):2*26 -3 = 27*13-3

3. 1+2+3+...100=(1+100):2*100= 101* 50

4. 13+14+15+...88= 1 +2+3+..12+13+14+...88 - (1+2+3+..12) = (1+ 88):2*88 -(1+12):2*12 = 89*44-

13*6= 2[(89*2) -39] = 2*(178-39) =2* 139 = 278

Explicație pas cu pas: