1) 2(1+2+3+...+50)=2×50×51:2=50×51=2550
2) 1+2+3+4+...+101=101×102:2=10302:2=5151
2¹+2²+2³+....+2¹⁰¹=2⁵¹⁵¹
3)U(1991²⁰)=U(1)
U(1993²⁰)=U(1)
U(1995²⁰)=U(5)
1+1+5=7 => 1991²⁰+1993²⁰+1995²⁰nu este patrat perfect
deoare ce patratele perfecte se termina in 0,1,4,9,6,5.
Sper ca te-am ajutat.
