Hey, guys. I'm new to the whole calculus branch of mathematics (we've just started) and I'm utterly confused about some concepts. Initially, we had started working finding the slope of a tangent to a particular point on a curve via m= f(a+h)-(a)/ h and working it by subbing in the given point etc... now in another chapter, the equation for calculating the derivative function is given, f ' (x) = lim h-->0 f(x+h)-f(x)/ h .. I'm curios to know what's the difference.. just the a is replace by a different variable.