Let $f(x) = 3{\sin ^4}x + 10{\sin ^3}x + 6{\sin ^2}x - 3$, $x \in \left[ { - {\pi \over 6},{\pi \over 2}} \right]$. Then, f is :

Question

increasing in $\left( { - {\pi \over 6},{\pi \over 2}} \right)$

decreasing in $\left( {0,{\pi \over 2}} \right)$

increasing in $\left( { - {\pi \over 6},0} \right)$

decreasing in $\left( { - {\pi \over 6},0} \right)$

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