Differential Calculus
1.2,1 "Ordinaryt' Derivatives
Question: suppose we have a function of one variable: f (x). what does the derivative,
df / d x, do for us? Answer: It tells us how rapidly the function / (-r) varies when we change
the argument x by a tiny amount, dx:
(1.33)
Inwords: Ifwechangexbyanamountdx,then/ehangesbyanamountdf;thederivative
is the proportionality factor. Fot example. in Fig. 1.17(a),the function varies slowly with
x, and the derivative is correspondingly small. In Fig. l.l7(b), / inereases mpidly with x,
and the derivative is large, as you move away from x = 0.
Geomctrical Interpretation: The derivativedf /dx istlte slope of the graph of / versus x.