aaa=100a+10a+a=111a abcd=ab00+cd=100ab+cd abab=100ab+ab=101ab aa0bb=1000 x 11a+11b=11(1000a+b) (ab)^2=(10a+b)^2=100a^2+20a x b+b^2=20a(5a+b)+b^2 7) √(a2 x a4 +1)=√[(10a+2)(10a+4)+1]=√(100a^2+60a+8+1)=√(10a+3)^2=10a+3 10a+3∈N* 8) 252=2^2 x 3^2 x 7 factorii lui 252 care au 2 cifre sunt: 18; 14 12; 21 14; 18 singura pereche cu numere rasturnate este 12;21 12 x 21 =252 xyyx={1221;2112}
