Question

[Cao Ngọc Diệp]

Tim x 

 (x-1)+(x-2)+(x-3)+...+(x-19)+(x-20)=-610

help me

Ban nao co cach lam day du minh se tick cho

Answer 1

[Trần Minh Tuấn Kiệt]

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

\(x-1+x-2+x-3+...+x-20=-610\)

\(\left(20x\right)+\left(-1+-2+-3+...+-20\right)=610\)

\(\left(20x\right)+-210=610\)

\(\left(20x\right)-210=610\)

\(20x=610+210\)

\(20x=820\)

\(x=820:20\)

\(x=41\)