Question

Tìm x biết:

x+(x+1)+(x+2)+...+(x+19)+(x+20)=20

Answer 1

\(x+\left(x+1\right)+\left(x+2\right)+.......+\left(x+19\right)+\left(x+20\right)=20\)

\(\Leftrightarrow\left(x+x+...+x\right)+\left(1+2+.......+20\right)=20\)

\(\Leftrightarrow21x+210=20\)

\(\Leftrightarrow21x=-190\)

\(\Leftrightarrow x=\dfrac{-190}{21}\)

Answer 2

\(x+\left(x+1\right)+\left(x+2\right)+...+\left(x+19\right)+\left(x+20\right)=20\)