Question

доказать что выражение не зависит от переменной У

Answer 1

(у+3)/(y^2-3y)-y/(y^2-9)=(y+3)(y(y-3))-y/(y-3)(y+3)=((y+3)^2-y^2)/(y(y-3)(y+3)=
(y^2+6y+9-y^2)/y(y+3)(y+3)=(6y+9)/(y(y-3)(y+3)

3(2y+3)/y(y-3)(y+3) *(y^2+3y)/(2y+3)=3/(y-3)
 y/(3-y)+3/(y-3)=  y/(3-y)/(y3-y)=1