Răspuns :
0,2+0,4+0,6+...+1,8=
2/10+4/10+6/10+...+18/10=
(2+4+6+...+18)/10=
2(1+2+3+...+9)/10=
2(9×10:2)/10=
2(90:2)/10=
2×45/10=
90/10=9
===========================
2/10+4/10+6/10+...+18/10=
(2+4+6+...+18)/10=
2(1+2+3+...+9)/10=
2(9×10:2)/10=
2(90:2)/10=
2×45/10=
90/10=9
===========================