2 + 5y = 2 + 5y
4 - 25y^2 = (2 + 5y) (2 - 5y)
2 - 5y = 2 - 5y
the lcm is (2 + 5y) (2 - 5y) because (2 + 5y) (2 - 5y) contains a (2 + 5y) (to make 2 + 5y), a (2 + 5y) (2 - 5y) (to make 4 - 25y^2), and a 2 - 5y (to make 2 - 5y).
the lcm of 2 + 5y, 4 - 25y^2, and 2 - 5y is (2 + 5y) (2 - 5y) or just 4 - 25y^2
another way of saying would be that 2 + 5y is a factor of 4 - 25y^2 and 2 - 5y is a factor of 4 - 25y^2, so the lcm is just 4 - 25y^2