Răspuns:
1+3=4=2^2
1+3+5=9=3^2
1+3+5+7=16=4^2
1+3+5+7+9=25=5^2
2) se observa ca suma respectivelor nume sunt patrate perfecte
3) 1+3+5+7+....+19 in total 9 termeni
(1+19)*9/2=20*9/2=180/2 =90 suma acestor numere impare
4) 1+3+....+99 sunt 49 termeni
(49+1) *99/2=50*49/2=25*49=1225
