Tangent lines Recall: tangent line is the limit of secant line The tangent line to the curve y=f(x) at the point P(a,f(a)) is the line through P with slope.

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Tangent lines Recall: tangent line is the limit of secant line The tangent line to the curve y=f(x) at the point P(a,f(a)) is the line through P with slope provided that the limit exists. Remark. If the limit does not exist, then the curve does not have a tangent line at P(a,f(a)).

Tangent lines Ex. Find an equation of the tangent line to the hyperbola y=3/x at the point (3,1). Sol. Since the limit an equation of the tangent line is or simplifies to

Velocities Recall: instantaneous velocity is limit of average velocity Suppose the displacement of a motion is given by the function f(t), then the instantaneous velocity of the motion at time t=a is Ex. The displacement of free fall motion is given by find the velocity at t=5. Sol. The velocity is

Rates of change Let The difference quotient is called the average rate of change of y with respect to x. Instantaneous rate of change = Ex. The dependence of temperature T with time t is given by the function T(t)=t 3 -t+1. What is the rate of change of temperature with respective to time at t=2? Sol. The rate of change is

Definition of derivative Definition The derivative of a function f at a number a, denoted by is if the limit exists. Similarly, we can define left-hand derivative and right- hand derivative exists if and only if both and exist and they are the same.

Example Ex. Find the derivative given Sol. Since does not exist, the derivative does not exist.

Example Ex. Determine the existence of of f(x)=|x|. Sol. Since does not exist.

Continuity and derivative Theorem If exists, then f(x) is continuous at x 0. Proof. Remark. The continuity does not imply the existence of derivative. For example,

Interpretation of derivative The slope of the tangent line to y=f(x) at P(a,f(a)), is the derivative of f(x) at a, The derivative is the rate of change of y=f(x) with respect to x at x=a. It measures how fast y is changing with x at a.

Derivative as a function Recall that the derivative of a function f at a number a is given by the limit: Let the above number a vary in the domain. Replacing a by variable x, the above definition becomes If for any number x in the domain of f, the derivative exists, we can regard as a function which assigns to x.

Remark Some other limit forms

Example Find the derivative function of Sol. Let a be any number, by definition, Letting a vary, we get the derivative function

Other notations for derivative If we use y=f(x) for the function f, then the following notations can be used for the derivative: D and d/dx are called differentiation operators. A function f is called differentiable at a if exists. f is differentiable on [a,b] means f is differentiable in (a,b) and both and exist.

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