Ta có:\(\left(x-1\right)+\left(x-2\right)+...+\left(x-20\right)=-610\)
\(x-1+x-2+x-3+...+x-20=-610\)
\(\left(20x\right)+\left(-1+-2+-3+...+-20\right)=610\)
\(\left(20x\right)+-210=610\)
\(\left(20x\right)-210=610\)
\(20x=610+210\)
\(20x=820\)
\(x=820:20\)
\(x=41\)