# Definite and Indefinite intregrals.

1. Nov 30, 2004

### QuantumTheory

Ok.

Im' confused between the difference of definite and indefinite integrals.

$$\int\limits_a_b$$

$$\int$$

The first integral here which is $$\int\limits_a_b$$ is about area below a curve.

Where a and b is the difference of the area under the function f(x). The $$\int\$$ is just the whole of all of the f(x) dx on an area.

Consider we have an area under the curve.

We will call the function f(x) = $$x^2$$

The area under the curve is then defined as:

$$\int\limits_a_b f(x) dx = dL$$

The $$\int\limits_a_b$$ is defined as all of dx of the function f(x) from a to b.

dx is a small infinitely small piece of the area under the curve.

dL is defined as the area.

I do not understand the integral:

$$\int$$ , which has no limits (a to b).

I know that this integral is backwards differenatation and requires a constant (I don't know what "arbitary" means, I think it means "fixed"?)

Such that,

$$\int x^2$$ = $$1/3^2 + C$$

Thanks

Last edited: Nov 30, 2004
2. Nov 30, 2004

### QuantumTheory

OH!

I think it requires a constant because there is no limit! (like the area integral)
(No a to b)

Just popped in my head..am I right?

3. Nov 30, 2004

### mathman

The indefinite integral has the variable as part of the answer. the integral of x2 is x3/3 + c. (You can verify by taking the derivative with respect to x - the derivative of c is 0)

4. Nov 30, 2004

The indefinite integral allows the upper or lower limit of integration to vary, while definite integration both the upper and lower limits are fixed. Hence we have the fundamental theorem of calculus.

Hopw this helps

5. Nov 30, 2004

### dextercioby

The indefinite integral of a function (or the primitive) is nothing but the function you need to differentiate as to obtain the original function (a.k.a.the integrand).
The definite integral has the geometrical interpretation of the area under the graphic of the function which constitutes the integrand,and the Leibniz-Newton theorem establishes the connection between the two notions.
This is the simplest explanation one can give.