[tex]\displaystyle\bf\\a-2=b-a \Leftrightarrow a-2+a=b \Leftrightarrow a+a = b +2 \Leftrightarrow 2a=b+2,\\pentru~ca~2a~este~mereu~par~indiferent~daca~a~este~par~sau~impar~,\\iar~b+2~este~par~doar~daca~b~este~par~si~cum~b~este~prim~din~\\enunt \implies b = 2~(singurul~numar~prim~par).\\2a=2+2 =4 \implies a = 2[/tex]
