a) 1,2=12/10=6/5
0,75=75/100=15/20=3/4
4,12=412/100=206/50=103/25
b) 0,(3)=3/9=1/3
2,(36)=236-2/99=234/99=78/33
4,(125)=4125-4/999=4121/999
0,3(12)=312-3/990=309/990=103/330
8,0(6)=806-80/90=726/90=242/30
12,12(345)=1212345-1212/99900=1211133/99900=
=403711/33300
12) 2/n-5->echiunitara => 2=n-5 =>n=7
4/2n+1->echiunitara=> 4=2n+1 => 2n=5 => n=2,5 dar n apartine N-> fals
3n-4/n+12->echiunitara=> 3n-4=n+12 => 3n=n+16 => 2n=16=> n=8
13) 21/n-3=> 21<n-3 => n-3={22,23,24,25,...} => n={25,26,27,28,...}
2n+1/n+5=> 2n+1<n+5 => 2n<n+4 => n<4 => n={0,1,2,3}
20/3n+1=> 20<3n+1 =>19<3n > n={7,8,9,10,...}
