# Math Help - integration and the greatest function help exam in 7 hrs

1. ## integration and the greatest function help exam in 7 hrs

integrate f(x) from 0 to n. where n is a positive integer and f(x) is the greatest integer function.
I Know that i have to use the definiton of greatest integer function and break it into sum of the integrals how do i do this.

2. Originally Posted by myoplex11
integrate f(x) from 0 to n. where n is a positive integer and f(x) is the greatest integer function.
I Know that i have to use the definiton of greatest integer function and break it into sum of the integrals how do i do this.
F(b) - F(a) is the signed area, where a and b are the limits of integration (from a to b).

In this case, your b is n and 0 is a. Do you have a specific problem?

3. this is the problem we had on our practice exam

4. Originally Posted by myoplex11
integrate f(x) from 0 to n. where n is a positive integer and f(x) is the greatest integer function.
I Know that i have to use the definiton of greatest integer function and break it into sum of the integrals how do i do this.
Okay.

A defined function on a closed interval is Riemann integrable if and only if it is continous almost everywhere.

We we need to find,
$\int_0^n [ x ] dx$
Since it is continous almost everywhere we can use the subdivision rule,
$\sum_{k=1}^n \int_{k-1}^k [x] dx$
But,
$\int_{k-1}^k [x] dx =k-1$
Because in that $[x]=k-1$ on this interval.

Thus,
$\sum_{k=1}^n k-1=\frac{n(n-1)}{2}$

5. Originally Posted by AfterShock
F(b) - F(a) is the signed area, where a and b are the limits of integration (from a to b).

In this case, your b is n and 0 is a. Do you have a specific problem?
That theorem does not work. The fundamental theorem of calculus only applies when a function is countinous on the closed interval.

6. If you draw a graph for say n=8, you will see a series of seven ‘stair steps’.
The area under the ‘stairs’ is the sum of the areas of seven rectangles.
So 1+2+3…+7. To do it for n we get a sum of $\frac{{\left( {n - 1} \right)n}}{2}.$