For x {\displaystyle x} close to a {\displaystyle a} , The linear approximation L ( x ) {\displaystyle L(x)} to f ( x ) {\displaystyle f(x)} has form f ( x ) ≈ L ( x ) = f ( a ) + f ′ ( a ) ( x − a ) . {\displaystyle f(x)\thickapprox L(x)=f(a)+f'(a)(x-a).}
