(а² -4b²) / 2ab : (1/2b - 1/a) =
= [ (a²- (2b)²)/ 2ab ] : [ (а-2b) /2ab ]=
= [(a-2b)(a+2b)/ 2ab ] * [ 2ab/ (a-2b) ] =
= (a+2b) / 1 =
= a +2b
при а = 3 1/19 , b =5 9/19
3 1/19 + 2 * 5 9/19 = 3 1/19 + 2/1 * 104/19 =
= 3 1/19 + 208/19 =3 1/19 + 10 18/19 = 14