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1+3+5+7+....+99 este patrat perfect

Răspuns :

(1+2+3+..+99)-(2+4+6+...+98)= (99*100)/2 - 2(1+2+3+..+49)= 99*50-2*49*50/2= 99*50-49*50=50(99-49)= 50*50= 50^2 care e patrat perfect
e regula de la problema anterioara:
(1+99) x 49:2=100 x 50:2=5000:2=2500 adica 50 la a 2 a