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Irinadobreanu
a fost răspuns

1+2+3+...+11=a 9+10+11+...+18=b calculati a+b

Răspuns :

Cocirmariadenis

1 + 2 + 3 + ......+ 11 = a

a = 11 × ( 1 + 11 ) / 2

a = 11 × 12 / 2

a = 11 × 6

a = 66

_________

b = 9 + 10 + 11 + ..... + 18

b = ( 18 - 9 + 1 ) × ( 9 + 18 ) / 2

b = 10 × 27 / 2

b = 270 / 2

b = 135

______________

a + b = 66 + 135 = 201

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