Find the Interval(s) Where F Is Concave Down For $f ( x ) = - 4 x ^ { 4 } + 3 x ^ { 3 } - 5 x + 10$

Multiple Choice

Find the interval(s) where f is concave down for $f ( x ) = - 4 x ^ { 4 } + 3 x ^ { 3 } - 5 x + 10$

A) $\left( - \infty , \frac { 3 } { 8 } \right)$
B) (-?, 0) ? (3, ?)
C) $(\left. 0 , \frac { 3 } { 8 } \right)$
D) (-?, 0) ? $\left( \frac { 3 } { 8 } , \infty \right)$
E) (-?, 0)