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Calculaţi : a) 1+ 2+ 3+....... +157; c) 1 + 2 + 3 +...+ 206; b) 1+2+3+...... 174; d) 1 + 2 +3....... +325.​

Răspuns :

a. (157 × 158) :2 = 157×79=12.403

b. (206×207):2=207×103=21.321

c. (174×175):2= 175×87=15.225

d. (325×326):2=325×163=53.301

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