Answer
The solution below shows that $(x+y)^3$ is not equal to $x^3+y^3.$
Work Step by Step
Substituting $x=3$ and $y=4,$ the given expression, $
(x+y)^3
,$ evaluates to
\begin{array}{l}\require{cancel}
(3+4)^3
\\\\=
(7)^3
\\\\=
343
,\end{array}
while the given expression, $
x^3+y^3
,$ evaluates to
\begin{array}{l}\require{cancel}
3^3+4^3
\\\\=
27+64
\\\\=
91
.\end{array}