Question

2+4+8+...........+30 Ajutati.ma

Answer 1

2 + 4 + 6 +........... + 30 =

dam factor comun 2

2×(1 + 2 + 3 +........... + 15) =

in paranteza observam o suma Gauss, care are formula de calcul

S = [n(n+1)]:2,  unde n reprezinta ultimul termen al sumei

S = (15 × (15+1)]:2 = (15×16):2 = 120

2×(1 + 2 + 3 +........... + 15) = =2 × 120 = 240

2 + 4 + 6 +........... + 30 = 240