Question

x+2x+3x+.....+20x=210

Answer 1

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Ta có: \(x+2x+3x+....+20x=210\)

\(\Leftrightarrow x\left(1+2+3+...+20\right)=210\)

\(\Leftrightarrow\dfrac{20\cdot\left(20+1\right)}{2}x=210\)

\(\Rightarrow x=\dfrac{210\cdot2}{20\cdot\left(20+1\right)}=1\)

Vậy \(x=1\)

Answer 2

Làm dùm mình với

Answer 3

x+2x+3x+...+20x=210

x(1+2+3+...+20)=210

x105=210

x=2