Question 916854
Given:
(1) y^2 -25/y^2 -3y-10 
But I think you mean
(2) (y^2 -25)/(y^2 -3y-10), which makes all the difference in the world!
In (2) you can factor the numerator
(3) y^2 -25 = (y-5)*(y+5) and the denominator
(4) y^2 -3y-10 = (y-5)*(y+2)
Now place (3) and (4) into (2) to get
(5)(y^2 -25)/(y^2 -3y-10) = ((y-5)*(y+5))/((y-5)*(y+2)) or after cancellation of (y-5) we get
(6)(y^2 -25)/(y^2 -3y-10) = (y+5)/(y+2)
Answer: The given expression simplifies to (y+5)/(y+2).