a) [A₁A₅₀]= 2+4+6+...+98
S=2(1+2+3+..+49)
S=2*(1+49)*49/2
S=50*49= 2450
b) [M-mij lui [A₂₀A₂₁] => A₂₀M=MA₂₁ =[A₂₀A₂₁]/2= 48/2=24
[A₁M]= 2+4+...+24= 2(1+2+3...+12)=2*(1+12)*12/2= 13*12= 156
c)[A₅A₆]=8
Q-mij lui [A₅A₆] =>A₅Q=QA₆= A₅A₆/2=8/2=4
[A₄₅A₄₆]=48
P-mij lui [A₄₅A₄₆] =>A₄₅P=PA₄₆=A₄₅A₄₆/2= 48/2=24
QP=4+10+12+...+46+24= 24+4+2(5+23)*19/2=
=28 +28*19= 28(1+19)= 28*20= 560