Question

1+3+5+7+...+99
3+7+11+15+...+43
3+6+9+12+...+2019
va rog din suflet
​

Answer 1

1+3+5+7+...+99

1 = 2×0+1

3 = 2×1+1

5 = 2×2+1

___________

99 = 2×49+1

S = ( 2×0+1 ) + (2×1+1) + (2×2+1) + ... + ( 2×49+1 )

S = 2(1+2+...+49)+1×50

S = 2×49×50:2+50

S = 49×50+50

S = 2450 + 50

S = 2500

3+7+11+15+...+43

S = 43+39+35+...+3

2S = 46+46+46...+46

(43-3):4+1

2S = 46×11:2

S = 23×11

S = 253

3+6+9+12+...+2019

S = 3(1+2+3+...673)

673×674

S = ———————

2

453602

S = ———————

2

S = 3×226801

S = 680403