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

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

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

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

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

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

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

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

\(\Rightarrow x=14\)

Vậy x = 14

Ảnh hơi khó nhìn,bn chịu khó nha

​

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

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

1+2+3+...+x=210/2=105

(x+1).x/2=105

(x+1).x=105.2=210=15.14

Vậy x=14

X =14 với đúng

k Mình nha

x=8 bạn nhé

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

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

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

=x+1.x/2=105

(x+1)x=210

14.15=210

=>x=14

Vậy x=14

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

(x+1)x =210= 15.14

x =14

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

(1+2+3+4+........+x)   =210:2

1+2+3+4+........+x     =105

(x+1).x:2                   =105

(x+1)x                       = 210 =14.15

=>x=14

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

(x+1)x=210=15x14

x=14

​tick mình nhé

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

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

Vậy x = 14

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

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

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

n*(n+1)/2=105

n*(n+1)=210

n*(n+1)=20*21

vì n và n+1 là 2 số tự nhiên liên tiếp nên n=1

x=20