Antiderivatives or indefinite integrals, Slides of Calculus

Definite vs indefinite integral: is there a connection? The Area function. Given a continuous function f on [a,b], define its area function A(x) ...

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Antiderivatives or indefinite integrals
Definition
If Fand fare two functions on [a,b] such that
d
dx F(x) = F0(x) = f(x),
we say fis the derivative of F, and Fis an antiderivative of f.
For instance, we know that
d
dx sin x= cos x,
d
dx x3= 3x2
.
We say that
cos xand 3x2are the derivatives of sin xand x3respectively, or
sin xis an antiderivative of cos x,
x3is an antiderivative of 3x2.
Math 105 (Section 204) Definite and indefinite integrals, Fundamental theorem of calculus 2011W T2 1 / 8
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Antiderivatives or indefinite integrals

Definition

If F and f are two functions on [a, b] such that d dx F^ (x) =^ F^

′(x) = f (x), we say f is the derivative of F , and F is an antiderivative of f.

Antiderivatives or indefinite integrals

Definition

If F and f are two functions on [a, b] such that d dx F^ (x) =^ F^

′(x) = f (x), we say f is the derivative of F , and F is an antiderivative of f. For instance, we know that d dx sin^ x^ = cos^ x,^

d dx x

(^3) = 3x (^2).

We say that cos x and 3x^2 are the derivatives of sin x and x^3 respectively, or sin x is an antiderivative of cos x, x^3 is an antiderivative of 3x^2.

Examples of indefinite integrals : the power rule

The derivative identities d dx

[ (^) xa+ a + 1

]

= xa^ for a 6 = − 1 , d dx ln^ x^ =

x , may be rephrased as ∫ xa^ dx =

xa+ a + 1 +^ C^ if^ a^6 =^ −^1 , ln x + C if a = − 1.

Indefinite integrals: some more examples

Exponential and trigonometric functions

eax^ dx = e

ax ∫^ a^ +^ C^ , sin(ax) dx = − (^1) a cos(ax) + C , ∫ cos(ax) dx =^1 a sin(ax) + C , ∫ sec^2 ax dx =^1 a tan(ax) + C , ∫ sec(ax) tan(ax) dx =^1 a sec(ax) + C.

Definite vs indefinite integral: is there a connection?

The Area function

Given a continuous function f on [a, b], define its area function A(x) as the definite integral A(x) =

∫ (^) x a^ f^ (t)^ dt,^ a^ ≤^ x^ ≤^ b. In other words, A(x) is a function on [a, b] whose value at x is the signed area under the curve y = f (t) between t = a and t = x.

Computation of the area function: Example 1

Given a constant function f , its area function is

A. constant B. linear C. quadratic D. always positive

Area function: Example 2

For a linear function f (t) = mt + c, its area function on [0, b] is

A. constant B. linear C. quadratic D. always increasing

Area function: Example 2

For a linear function f (t) = mt + c, its area function on [0, b] is

A. constant B. linear C. quadratic D. always increasing

Question: What is the derivative of the area function of a linear function?