Răspuns :
9x 5(1+2+3+....+40):41=
9x 5(1+40)x40/2 :41=
9 x 5 x41x20 :41=
9x5 x20=
45x20= 900-este pp
30²=900
9x 5(1+40)x40/2 :41=
9 x 5 x41x20 :41=
9x5 x20=
45x20= 900-este pp
30²=900