Cho x1 + x2 + x3 + x4 + ................ + x49 + x50 + x51 = 0 và x1 + x2 = x3 + x4 = x5 + x6 = ..... = x47 + x48 = x49 + x50 = x50 + x51 = 1. Tính x50?

Câu 21:  Cho ${\mathrm{x}}_1$ + ${\mathrm{x}}_2$ + ${\mathrm{x}}_3$ + ${\mathrm{x}}_4$ + ................ + ${\mathrm{x}}_{49}$  + ${\mathrm{x}}_{50}$  + ${\mathrm{x}}_{51}$ = 0

và ${\mathrm{x}}_1$ + ${\mathrm{x}}_2$ = ${\mathrm{x}}_3$ + ${\mathrm{x}}_4$ = ${\mathrm{x}}_5$ + ${\mathrm{x}}_6$ = ..... = ${\mathrm{x}}_{47}$ + ${\mathrm{x}}_{48}$ = ${\mathrm{x}}_{49}$ + ${\mathrm{x}}_{50}$ = ${\mathrm{x}}_{50}$ + ${\mathrm{x}}_{51}$ = 1. Tính ${\mathrm{x}}_{50}$?