Question

Tìm x

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

ai nhanh và trả lời đúng nhất mình tik cho!!!!!

Answer 1

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

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

suy ra x=14

học tốt nhé bn

Answer 2

\(2+4+6+8+...+2x=210\)

\(\frac{(2\chi+2)\times\chi}{2}=210\)

\(2\left(x+1\right)x=210\cdot2=420\)

\(x\left(x+1\right)=420:2=210\)

\(x=14\)

Answer 3

2+ 4+ 6+...+( 2X- 2)+ 2X= 210.

=> 2[ 1+ 2+ 3+...+( X- 1)+ X]= 210.

=> 1+ 2+ 3+...+( X- 1)+ X= 210: 2.

=> 1+ 2+ 3+...+( X- 1)+ X= 105.

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

=>( X+ 1)x X= 105x 2.

=>( X+ 1)x X= 210.

=>( X+ 1)x X= 15. 14.

=> X= 14.

Vậy X= 14.