Using the results of questions 8, 9, 10a and 10b, conclude that the set of trigonometric polynomials in two variables is dense in $\mathscr { C } _ { \text {per} } \left( \mathbb { R } ^ { 2 } \right)$.
Using the results of questions 8, 9, 10a and 10b, conclude that the set of trigonometric polynomials in two variables is dense in $\mathscr { C } _ { \text {per} } \left( \mathbb { R } ^ { 2 } \right)$.