Question

Aratati ca x apartine R astfel incat 12x si xx (cu bara deasupra) sa fie prime intre ele. E urgent!

Answer 1

12x = 120+x

xx = 11•x

(120+x)/(11x) = 120/11x +x/11x =

= 120/11x + 1/11 = (120/x+1)/11

120/x+1 ≤ 121

=> 120/x+1 nu aparține {11,121}

(1) 120/x+1 ≠ 11 => 120/x ≠ 10 => x ≠ 12

(2) 120/x+1 ≠ 121 => 120/x ≠ 120 => x ≠ 1

=> x ∈ {2,3,4,5,6,7,8,9}