Question 152567
First use the formula 
{{{(a+b)^2=a^2+2ab+b^2}}}
and
{{{(a-b)^2=a^2-2ab+b^2}}}
to expand,
then combine like terms.
{{{(x+y)^2+(x-3y)^2}}}
= {{{x^2+2xy+y^2+x^2-2x*(3y)+(3y)^2}}}
= {{{x^2+2xy+y^2+x^2-6xy+9y^2}}}
= {{{2x^2-4xy+10y^2}}}