Question

1o2o3o....o54
xoy= x+y+7

Answer 1

Răspuns:

15870

Explicație pas cu pas:

1o2o3o....o54 = ?

xoy= x+y+7

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1 o 2 = 1+2+7 = 10

10 o 3 = 10+3+7 = 20 =>

1 o 2 o 3 =20

20 o 4 = 20+4+7 = 31 =>

1 o 2 o 3 o 4 = 31

31 o 5 = 31+5+7 = 43 =>

1 o 2 o 3 o 4 o 5 = 43

43 o 6 = 43+6+7 =56 =>

1 o 2 o 3 o 4 o 5 o 6 = 56

...........................................

20-10 = 10 ; 31-20 = 11 ; 43-31 = 12 ; 56-43 = 13

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1o2o3o....o54 = 10+(10+11+12+13+.......+61) =

= 10+(10+61)·(61-10+1):2 = 10+610·52:2 =

= 10+610·26 = 10+15860 = 15870

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