Question

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

tìm x

Answer 1

 

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

(x+1)x =210= 15.14

x =14

Answer 2

(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

 

Answer 3

 

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

(x+1)x=210=15x14

x=14

​tick mình nhé