Show that for all $a \in \mathbb { R }$, $$\int _ { 0 } ^ { a } \sin \left( x ^ { 2 } \right) \mathrm { d } x = \sum _ { n = 0 } ^ { + \infty } ( - 1 ) ^ { n } \frac { a ^ { 4 n + 3 } } { ( 2 n + 1 ) ! ( 4 n + 3 ) }$$