Question

Tìm x biết 2+4+6+8+...+2x=210

Answer 1

= 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

Answer 2

= 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