Similar to 1.6.24:
1.11 Find the limit.
limx-->+infinity [sqrt (x^2 + 5x) - sqrt (x^2 + 3x)]
Hint: Begin by using
sqrt a - sqrt b = (sqrt a - sqrt b) (sqrt a + sqrt b)/(sqrt a + sqrt b), and
(sqrt a - sqrt b) (sqrt a + sqrt b)/(sqrt a + sqrt b) = (a - b)/(sqrt a + sqrt b).
