(x-2)(x-5) must be positive since you cannot take the square root of a negative number.
So (x-2)(x-5) > 0
(x-2)(x-5) has the zeros x = 2 or x = 5. (x-2)(x-5) is positive when either x < 2 or x > 5. You can see this you plug in values such as x = 1 or x = 6.
(x-2)(x-5) is negative when 2 < x < 5. You can see this you plug in values such as x = 3 or x = 4.