Let x and y be real numbers such that xy=9. Find the set of all possible values of x+y. Enter your answer in interval notation.
+23246 Find the set of all possible values of x + y that fulfill x·y = 9.
When x·y = 9 . ---> y = 9 / x and x + y = x + 9 / x ---> x + y = (x2 + 9) / x
The function: f(x) = (x2 + 9) / x
-- has a minimum in the first quadrant at 6, so its positive values are in [6, infinity)
-- has a maximum in the thrid quadrant at -6, so its negative values are in (- infinity, -6]
