Question 148579
{{{(r+s)^2+(r-s)^2}}}={{{(r+s)(r+s)+(r-s)(r-s)}}}


Do (r+s)(r+s)
{{{r^2+2sr+s^2}}}


Do (r-s)(r-s)
{{{r^2-2sr+s^2}}}


Now add them
{{{r^2+2sr+s^2+r^2-2sr+s^2}}}


Combine like terms
{{{2r^2+2s^2}}}