Write the value of limx→0f(x)−f(x)x−c
Since we know that,
dx(f(x))=limh→0f(x+h)−f(x)h
Let,
h = x - c and f(x) = c
If h→0 then x→c
Therefore,
ddx(c)=limx→ef(x+c−x)−f(c)x−c
=limx→ef(x)−f(c)x−c
=f′(c)