Solve the problem.
-Find the points where the graph of the function have horizontal tangents. $$f ( x ) = x ^ { 3 } - 21 x$$
A) $( \sqrt { 7 } , - 42 \sqrt { 7 } )$
B) $( - \sqrt { 7 } , 42 \sqrt { 7 } ) , ( 0,0 ) , ( \sqrt { 7 } , - 42 \sqrt { 7 } )$
C) $( - 7 , - 196 ) , ( \sqrt { 7 } , 196 )$
D) $( - \sqrt { 7 } , 14 \sqrt { 7 } ) , ( \sqrt { 7 } , - 14 \sqrt { 7 } )$

Question

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The Answer of Solve the problem.
-Find the points where the graph of the function have horizontal tangents. $$f ( x ) = x ^ { 3 } - 21 x$$
A) $( \sqrt { 7 } , - 42 \sqrt { 7 } )$
B) $( - \sqrt { 7 } , 42 \sqrt { 7 } ) , ( 0,0 ) , ( \sqrt { 7 } , - 42 \sqrt { 7 } )$
C) $( - 7 , - 196 ) , ( \sqrt { 7 } , 196 )$
D) $( - \sqrt { 7 } , 14 \sqrt { 7 } ) , ( \sqrt { 7 } , - 14 \sqrt { 7 } )$

Solve the Problem f(x)=x3−21xf ( x ) = x ^ { 3 } - 21 xf(x)=x3−21x

Solve the Problem $f ( x ) = x ^ { 3 } - 21 x$