Ta có : x1 + x2 + x3 + x4 + .......... +x49 + x50 + x51 = 0
<=> (x1 + x2) + (x3 + x4) + .......... + (x49 + x50) + x51 = 0
<=> 1 x 25 + x51 = 0
=> x51 = 0 - 25
=> x51 = -25
x1+x2+...+x50+x51=0
=> (x1+x2)+(x3+x4) +....+x51=0
=> 1 x 25 + x51 =0
=>25 +x51=0
=> x51= 0-25
=>x51 =-25