Also 
15
S
4
0
2

′′
=
>



 Therefore, by second derivative
test, 
x =215
 is the point of local minima of S Hence the sum of squares of numbers is
minimum when the numbers are 15
2  and 
15
15
15
2
2
−
= Remark Proceeding as in Example 34 one may prove that the two positive numbers,
whose sum is k and the sum of whose squares is minimum, are 
2and
2
k
k