Explicație pas cu pas:
(1+2+3+.....+16)-(1+2+3+....+10)=
(16×17):2–(10×11):2=
8×17–5×11=
136–55=81
(1+2+3+....+26)–(1+2+3+......+20)=
(26×27)÷2–(20×21)÷2=
13×27–10×21=
351–210=141
56+51=107
107×3=321
116+111=227
227×3=681
Sunt in doua moduri.
Sper ca te-am ajutat!
