Limit definition of the Derivative of a function:[tex] \lim_{h \to 0} \frac{f(x+h)-f(x)}{h} [/tex] At x = a:[tex] \lim_{h \to0} \frac{f(a+h)-f(a)}{h} [/tex]
If: h = x -π/4, we will have:[tex] \lim_{h \to \pi /4} \frac{tan ( \pi /4 +h)-1}{h} [/tex] When we compare it with a limit definition:
f( x )= tan x
f( a ) = 1
tan ( a ) = 1, a = π/4
