Răspuns :
Răspuns:
Explicație pas cu pas:
9×(5+10+15...+200):41
5+10+15...+200 = 40*(5 + 200)/2 = 40*205/2 = 4100
9 x 4100 : 41 = 9 x 100 = 900 = 30^2 patrat perfect
9×(5+10+5+15+....+200):41=
=9×5×(1+2+3+....+40):41=
=45×(40×41)/2:41=
=45×20×41:41=
=45×20=900=30²-patrat perfect