Use the Definition of Derivative $\lim _ { h \rightarrow 0 } \frac { f ( x + h ) - f ( x ) } { h }$

Essay

Use the definition of derivative: $\lim _ { h \rightarrow 0 } \frac { f ( x + h ) - f ( x ) } { h }$ to find $f ^ { \prime } ( x ) \text {, if } f ( x ) = \frac { 1 } { x ^ { 2 } }$