Find All the Critical Numbers of the Function $f ( x ) = 2 x ^ { 2 } - 8 x + 7$

Multiple Choice

Find all the critical numbers of the function $f ( x ) = 2 x ^ { 2 } - 8 x + 7$ .

A) -7
B) $- \frac { 7 } { 2 }$
C) 2
D) None