Consider the two numbers be
and
.
The sum of two positive numbers is
.


Consider the function be the sum of the squares of two numbers is
.

The smallest number is possible when first derivative function becomes zero.
\Apply derivative on each side with respect to
.

Equate
to zero.

Substitute
in
.

Therefore the smallest value of sum of the squares of two numbers is
.
The smallest value of sum of the squares of two numbers is
.