Question

tìm x biết 

x + 2x + 3x +....+100x = -213

Answer 1

\(x+2x+3x+...+100x=-213\)

\(\Leftrightarrow x.\left(1+2+3+..+100\right)=-213\)

\(\Leftrightarrow x.[\frac{\left(100+1\right).100}{2}]=-213\)( áp dụng dãy số cách đều )

\(\Leftrightarrow x.5050=-213\)

\(\Leftrightarrow x=\frac{-213}{5050}\)

Answer 2

x + 2x + 3x + ... + 100x = -213

100x + 5050 = -213

100x = -213 - 5050 = -5263

x = -5263 : 100

x = -52,63

Answer 3

\(x+2x+3x+...+100x=-213\)

\(\Rightarrow x\times\left(1+2+3+...+100\right)=-213\)

\(\Rightarrow x\times5050=-213\)

\(\Rightarrow x=\frac{-213}{5050}\)

Vậy ...

Answer 4

\(x+2x+3x+...+100x=-213\)

\(\left(x+x+x+...+x\right)\left(1+2+3+...+100\right)=-213\)

\(100x\cdot100=-213\)

\(100x=\frac{-213}{100}\)

\(x=-213\)