In the interval $( 0,2 \pi )$, the function $\sin \left( \frac { 1 } { x ^ { 3 } } \right)$ (a) never changes sign (b) changes sign only once (c) changes sign more than once, but finitely many times (d) changes sign infinitely many times.
(d) $\sin \left( \frac { 1 } { x ^ { 3 } } \right)$ changes sign at the points $( n \pi ) ^ { \frac { - 1 } { 3 } }$ for all $n \geq 1$.
In the interval $( 0,2 \pi )$, the function $\sin \left( \frac { 1 } { x ^ { 3 } } \right)$\\
(a) never changes sign\\
(b) changes sign only once\\
(c) changes sign more than once, but finitely many times\\
(d) changes sign infinitely many times.