[tex]\displaystyle\\
x+(2x-1)+(3x-2)+(4x-3)+\cdots+(51x-50)=51\\\\
(x+2x+3x+4x+\cdots +51x)-(1+2+3+4+\cdots +50) =51\\\\
x(1+2+3+4+\cdots +51) -(1+2+3+4+\cdots +50)=51\\\\
x(1+2+3+4+\cdots +51) = 51 +(1+2+3+4+\cdots +50)\\\\
x(1+2+3+4+\cdots +51) = 1+2+3+4+\cdots +50+51\\\\
x(1+2+3+4+\cdots +51) = 1+2+3+4+\cdots +51\\\\
x = \frac{ 1+2+3+4+\cdots +51}{1+2+3+4+\cdots +51} = \boxed{1}[/tex]