Find the Largest Open Interval Where the Function Is Changing $f ( x ) = \frac { 1 } { 4 } x ^ { 2 } - \frac { 1 } { 2 } x$

Multiple Choice

Find the largest open interval where the function is changing as requested.
-Increasing $f ( x ) = \frac { 1 } { 4 } x ^ { 2 } - \frac { 1 } { 2 } x$

A) $( - \infty , \infty )$
B) $( 1 , \infty )$
C) $( - 1,1 )$
D) $( - \infty , - 1 )$