Consider the two expressions $(x + y)^2$ and $x^2 + y^2$. Grogg thinks that these two expressions are equal for all real numbers $x$ and $y,$ but Lizzie disagrees! Let's get to the bottom of it. a) Evaluate $(x + y)^2$ and $x^2 + y^2$ when $x = 5$ and $y = 12.$

b) For which values of $x$ and $y$ does $(x + y)^2$ equal $x^2 + y^2?$ For which values of $x$ and $y$ does $(x + y)^2$ not equal $x^2 + y^2?$

(only need help for the second part)