Answer
The solution below shows that $(x+y)^2$ is not equal to $x^2+y^2.$
Work Step by Step
Substituting $x=3$ and $y=4,$ the given expression, $
(x+y)^2
,$ evaluates to
\begin{array}{l}\require{cancel}
(3+4)^2
\\\\=
(7)^2
\\\\=
49
,\end{array}
while the given expression, $
x^2+y^2
,$ evaluates to
\begin{array}{l}\require{cancel}
3^2+4^2
\\\\=
9+16
\\\\=
25
.\end{array}