Wednesday, October 10, 2012

Limit of Riemann Sums

Introduction to limit of Riemann sums:
Real analysis the Riemann integral is one of the branches of mathematics. The easiest integral is Riemann integrals. For a great many functions, the Riemann integral can also be readily evaluated by using the fundamental theorem of calculus by numerical integration. It is unsuitable for many theoretical purposes. In this article, we shall discuss about limit of Riemann sums.

Riemann Sums, and Midpoint Integral Formulas:

The  Riemann sum of the given function f(x) is         `sum_(k=1)^n f [t_k] Delta x_k ` . .

The Riemann sums exist the  max `Deltax->0` . This limits is riemann integralof f(x) over the interval [a,b].

Limit of Riemann Sums - Problems:
Limit of Riemann sums - problem 1:

Find the Riemann sum of the given function `int_0^3 sqrt(9-x^2)` dx .

Solution:

Given function is  `int_0^3 sqrt(9-x^2)` dx .

general formula for Riemann sum is  ` int_a^b f(x) dx = lim_(n->oo) sum_(i=1)^n sqrt f(x)`  .

`int_0^3 sqrt(9-x^2)` dx .   = ` lim_(n->oo) 3/n sum_(i=1)^n sqrt(9-((3i)/n)^2)` . .

Riemann integral sum is   ` lim_(n->oo) 3/n sum_(i=1)^n sqrt(9-((3i)/n)^2)` . .

Limit of Riemann sums - problem 2:

Determine the Riemann integral sum of  (4x4)  with the limits 0 to 2

Solution:

The  integral function is, `int_0^2` (4x4) dx.

`int_0^2`(4x4) dx =`int_0^2`4x4 dx

=`int_0^2`4x4 dx

= `[4(x^5/5)]_0^2` +

We know the numerical integral `int_a^b`f(x) dx = F(b) - F(a).

= `(4/5)` 25 - `(4/5)` 05

= `(4/5)` 32 - 0

= `(4/5)` 32

=  `128/5`.

Answer: `int_0^2`(4x4) dx = ` 128/5` .

Limit of Riemann sums - problem 3:

Find the value of numerical integral (4x4 + x2)  with the limits 0 to 2

Solution:

The numerical integral function is, `int_0^2` (4x4 + x2) dx.

`int_0^2`(4x4 + x2) dx =`int_0^2`4x4 dx +`int_0^2` x2 dx.

=`int_0^2`4x4 dx + `int_0^2` x2 dx.

= `[4(x^5/5)]_0^2` + `[(x^3/3)]_0^2`

We know the numerical integral `int_a^b`f(x) dx = F(b) - F(a).So,

= `(4/5)` 25 - `(4/5)` 05+ `(1/3)` 23 - `(1/3)` 03

= `(4/5)` 32 - 0 + `(1/3)` 8 - 0

= `(4/5)` 32+ `(1/3)` 8

= `128/5 + 8/3`

Take lcm for 5 and 3

= `[(128 xx 3) + (8 xx 5)]/15 `

= `(384 + 40)/15 `

= `424/15`

Answer: `int_0^2`(4x4 + x2) dx = `28 4/15` .

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