This is the best I got
Step-by-step explanation:
The term "integral" can refer to a number of different concepts in mathematics. The most common meaning is the the fundamenetal object of calculus corresponding to summing infinitesimal pieces to find the content of a continuous region. Other uses of "integral" include values that always take on integer values (e.g., integral drawing, integral graph), mathematical objects for which integers form basic examples (e.g., integral domain), and particular values of an equation (e.g., integral curve),
In calculus, an integral is a mathematical object that can be interpreted as an area or a generalization of area. Integrals, together with derivatives, are the fundamental objects of calculus. Other words for integral include antiderivative and primitive. The process of computing an integral is called integration (a more archaic term for integration is quadrature), and the approximate computation of an integral is termed numerical integration.
The Riemann integral is the simplest integral definition and the only one usually encountered in physics and elementary calculus. In fact, according to Jeffreys and Jeffreys (1988, p. 29), "it appears that cases where these methods [i.e., generalizations of the Riemann integral] are applicable and Riemann's [definition of the integral] is not are too rare in physics to repay the extra difficulty."
The Riemann integral of the function f(x) over x from a to b is written
int_a^bf(x)dx.
(1)
Note that if f(x)=1, the integral is written simply
int_a^bdx
(2)
as opposed to int_a^b1dx.
Every definition of an integral is based on a particular measure. For instance, the Riemann integral is based on Jordan measure, and the Lebesgue integral is based on Lebesgue measure. Moreover, depending on the context, any of a variety of other integral notations may be used. For example, the Lebesgue integral of an integrable function f over a set X which is measurable with respect to a measure mu is often written
int_Xf(x)dmu.
(3)
In the event that the set X in () is an interval X=[a,b], the "subscript-superscript" notation from (2) is usually adopted. Another generalization of the Riemann integral is the Stieltjes integral, where the integrand function f defined on a closed interval I=[a,b] can be integrated against a real-valued bounded function alpha(x) defined on I, the result of which has the form
intf(x)dalpha(x),
(4)
or equivalently
intfdalpha.
(5)
Yet another scenario in which the notation may change comes about in the study of differential geometry, throughout which the integrand f(x)dx is considered a more general differential k-form omega=f(x)dx and can be integrated on a set X using either of the equivalent notations
int_Xomega=int_Xfdmu,
(6)
where mu is the above-mentioned Lebesgue measure. Worth noting is that the notation on the left-hand side of equation () is similar to that in expression () above.
There are two classes of (Riemann) integrals: definite integrals such as (5), which have upper and lower limits, and indefinite integrals, such as
intf(x)dx,
(7)
which are written without limits. The first fundamental theorem of calculus allows definite integrals to be computed in terms of indefinite integrals, since if F(x) is the indefinite integral for f(x), then
int_a^bf(x)dx=F(b)-F(a).
(8)
What's more, the first fundamental theorem of calculus can be rewritten more generally in terms of differential forms (as in () above) to say that the integral of a differential form omega over the boundary partialOmega of some orientable manifold Omega is equal to the exterior derivative domega of omega over the interior of Omega, i.e.,
int_(partialOmega)omega=int_Omegadomega.
(9)
Written in this form, the first fundamental theorem of calculus is known as Stokes' Theorem.
Since the derivative of a constant is zero, indefinite integrals are defined only up to an arbitrary constant of integration C, i.e.,
intf(x)dx=F(x)+C.
(10)
Wolfram Research maintains a web site http://integrals.wolfram.com/ that can find the indefinite integral of many common (and not so common) functions.
Differentiating integrals leads to some useful and powerful identities. For instance, if f(x) is continuous, then
d/(dx)int_a^xf(x^')dx^'=f(x),
(11)
which is the first fundamental theorem of calculus. Other derivative-integral identities include
d/(dx)int_x^bf(x^')dx^'=-f(x),
(12)
the Leibniz integral rule
d/(dx)int_a^bf(x,t)dt=int_a^bpartial/(partialx)f(x,t)dt
(13)
(Kaplan 1992, p. 275), its generalization
d/(dx)int_(u(x))^(v(x))f(x,t)dt=v^'(x)f(x,v(x))-u^'(x)f(x,u(x))+int_(u(x))^(v(x))partial/(partialx)f(x,t)dt
(14)
(Kaplan 1992, p. 258), and
d/(dx)int_a^xf(x,t)dt=1/(x-a)int_a^x[(x-a)partial/(partialx)f(x,t)+(t-a)partial/(partialt)f(x,t)+f(x,t)]dt,
(15)
as can be seen by applying (14) on the left side of (15) and using partiall integration.
