131 e nr prim
abba= 1000a+100b+10b+a= 1001a+110b= 11(91a+10b)
abba div cu 131 => 91a+10b div cu 131
daca 91a+10b=1*131
=> abba= 11*131= 1441
daca 91a+10b= 2*131
=> abba= 11* 262=2882
daca 91a+10b=3*131
=>abba= 11*393=4323 nu mai e de forma abba
deci abba ∈{1441,2882} doua solutii
2) 13x²= 117 |:13
x²= 9
|x|=3
x=3 sau x=-3 doua solutii
O zi buna!
