[tex]\overline {2,1(a)}+\overline{2,a(1)}=\overline{a,1(2)}+\overline{1,a(2)}[/tex]
[tex]\frac{\overline{21a}-21}{90} +\frac{\overline{2a1}-\overline{2a}}{90} =\frac{\overline{a12}-\overline{a1}}{90} +\frac{\overline{1a2}-\overline{1a}}{90}[/tex]
- Avem acelasi numitor, il eliminam si scriem numerele in baza 10, vom obtine:
200+10+a-21+200+10a+1-20-a=100a+10+2-10a-1+100+10a+2-10-a
411-41+10a=99a+103
267=89a
a=267:89=3
a=3
