А
(a+3)/a(a-3)+(a-3)/3(a-3)=(3a+9+a²-9a)/3a(a-3)=(a²-6a+9)/3a(a-3)=
=(a-3)²/3a(a-3)=(a-3)/3a
б
(b-4)/2(b-2)+2/b(b-2)=(b²-4b+4)/2b(b-2)=(b-2)²/2b(b-2)=(b-2)/2b
в
2/x(x=2y)+1/y(x+2y)=(2y+x)/xy(x+2y)=1/xy