Mark M. answered 12/10/22
Retired math prof. Calc 1, 2 and AP Calculus tutoring experience.
xy = 289 So, y = 289/x
Minimize S = x + y = x + 289x-1
S' = 1 - 289/x2 = (x2 - 289) / x2
S' = 0 when x = 17 or -17
By assumption, x is positive. So, minimum when x = 17 and y = 17.