Solve the Initial-Value Problem $$y ^ { tt } + 16 y = 0 , y \left( \frac { \pi } { 4 } \right) = 0 , y ^ { t } \left( \frac { \pi } { 4 } \right) = 1$$

Solve the initial-value problem. $$y ^ { tt } + 16 y = 0 , y \left( \frac { \pi } { 4 } \right) = 0 , y ^ { t } \left( \frac { \pi } { 4 } \right) = 1$$