n=(5+10+15+...+275) (1/1×6+1/6×11+1/11×16+...+1/51×56)
n=5(1+2+3+….+55)( 1/1×6+1/6×11+1/11×16+...+1/51×56)
n=(55•56/2)•( 5/1×6+5/6×11+5/11×16+...+5/51×56)
2n=55•56•(1/1-1/6+1/6-1/11+1/11-1/16+…..+1/51-1/56)
2n=55•56•(1/1-1/56)
2n=55•56•55/56
2n=55², este patrat perfect
