\(2+4+6+...+2x=210\)

\(\Rightarrow2\left(1+2+3+...+x\right)=210\)

\(\Rightarrow1+2+3+...+x=210\div2\)

\(\Rightarrow1+2+3+...+x=105\)

\(\Rightarrow x+\left(x+1\right)\div2=105\)

\(\Rightarrow x+\left(x+1\right)=105.2\)

\(\Rightarrow x+\left(x+1\right)=210\)

\(\Rightarrow x+\left(x+1\right)=14.15\)

\(\Rightarrow x=14\)

Vậy x = 14

Ảnh hơi khó nhìn,bn chịu khó nha

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= 2.(1+2+3+4+.....+x)=210

=1+2+3+4+........+x=210:2

=1+2+3+4+....+x=105

=(x+1).x:2=105

=(x+1).x=105.2

=(x+1).x=210

=(x+1).x=14.15

Vay x=14

= 2.(1+2+3+4+.....+x)=210

=1+2+3+4+........+x=210:2

=1+2+3+4+....+x=105

=(x+1).x:2=105

=(x+1).x=105.2

=(x+1).x=210

=(x+1).x=14.15

Vay x=14

= 2.(1+2+3+4+.....+x)=210

=1+2+3+4+........+x=210:2

=1+2+3+4+....+x=105

=(x+1).x:2=105

=(x+1).x=105.2

=(x+1).x=210

=(x+1).x=14.15

Vay x=14

=» 2.1+2.2+2.3+2.4+.....+2x = 210

=» 2.(1+2+3+4+...+x) =210

=» 2.[x. (x +1 ) /2 =210

=» x.( x+1 ) =210

hay x.(x+1) =14.(14+1)

=» x= 14

Chúc bạn làm bài tốt =))

Ngu ngu ngu !

2+4+6+8+...+2x=210

=>2.1+2.2+2.3+2.4+...+2.x=210

=>2.(1+2+3+4+...+x)=210

=>1+2+3+4+...+x=210:2

=>1+2+3+4+...+x=105

=>x=14

2+4+6+8+...+2x=210

=>2.1+2.2+2.3+2.4+...+2.x=210

=>2.(1+2+3+4+...+x)=210

=>1+2+3+4+...+x=210:2

=>1+2+3+4+...+x=105

=>x=14

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

2*(x+1)*x/2=210

(x+1)x=210

x=14