\(2+4+6+8+...+2x=210\)
\(2\left(1+2+3+...+x\right)=210\)
\(2\left(\frac{x\left(x+1\right)}{2}\right)=210\)
\(\frac{2x\left(x+1\right)}{2}=210< =>x\left(x+1\right)=210\)
\(< =>x\left(x+1\right)=14,15\)
\(< =>x=14\)
\(2+4+6+8+...+2x=210\)
\(2\left(1+2+3+.....+x\right)=210\)
\(2\left(\frac{x\left(x+1\right)}{2}\right)=210\)
\(\frac{2x\left(x+1\right)}{2}=210\)\(\Leftrightarrow x\left(x+1\right)=210\)
\(\Leftrightarrow x\left(x+1\right)=14.15\)
\(\Rightarrow x=14\)
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