# Math Help - LRAM and RRAM??

1. ## LRAM and RRAM??

I don't get this,...

Use upper&lower sums to approx. the area of the region using the indicated number of subintervals(of equal length)

$y = 1/x$

It starts at 1 and ends at 2.. There are 5 squares..

What am I suppose to do?? Submation? I ended up getting lost.. Before I started it I got 1/(5+i) and had no idea how to use the submation.. Help!!

2. Originally Posted by elpermic
I don't get this,...

Use upper&lower sums to approx. the area of the region using the indicated number of subintervals(of equal length)

$y = 1/x$

It starts at 1 and ends at 2.. There are 5 squares..

What am I suppose to do?? Submation? I ended up getting lost.. Before I started it I got 1/(5+i) and had no idea how to use the submation.. Help!!

Draw a picture!

First, plot the function 1/x on the interval [1,2].

What the question is asking is for you to draw 5 rectangles of equal width 'under' the curve. So the base of the first rectangle will go from 1 to 1.2, the second from 1.2 to 1.4, and so on.

For the upper sum, the height of each rectangle will be the value of the function evaluated at the left-most part of the rectangle.

For the upper sum, the height of each rectangle will be the value of the function evaluated at the right-most part of the rectangle.

3. I still don't get it...

The answers online shows that it is doing a sequence like this..:

$s(5) = 1/(6/5) x (1/5) + 1/(7/5) x (1/5) .. all the way until 9$

I am guessing that 1/5 is delta x.. But where does the 1/(6/5) come from??

EDIT: So 1/(6/5) would be 1.2, then 1.4, 1.6, 1.8, .5?

I don't get it how it becomes 1/(6/5) x (1/5)

Is it the f(Xi) x delta x???

4. Originally Posted by elpermic
I still don't get it...

The answers online shows that it is doing a sequence like this..:

$s(5) = 1/(6/5) x (1/5) + 1/(7/5) x (1/5) .. all the way until 9$

I am guessing that 1/5 is delta x.. But where does the 1/(6/5) come from??

EDIT: So 1/(6/5) would be 1.2, then 1.4, 1.6, 1.8, .5?

I don't get it how it becomes 1/(6/5) x (1/5)

Is it the f(Xi) x delta x???
f(x)=1/x, so f(1.2)=1/(6/5)

This is the height of your first rectangle. its width (like all the others) is 1/5. so its area is 1/6.

The height of the second rectangle is f(1.4), width is 1/5.

This is how you get the area of each rectangle. Add up the five areas and you have the sum you are looking for.

5. So then..

Would RRAM be like this??

f(Xi) x delta x each square??

And then LRAM would be the same exact thing except you add a +1 into it??

Sorry, but I still odn't understand the concept..

6. Originally Posted by elpermic
So then..

Would RRAM be like this??

f(Xi) x delta x each square??

And then LRAM would be the same exact thing except you add a +1 into it??

Sorry, but I still odn't understand the concept..
I am not familiar with the RRAM and LRAM acronyms.

Perhaps wikipedia can explain it better than I can:
Riemann sum - Wikipedia, the free encyclopedia

A bit down the page under lower and upper sums there is a nice example. The upper sum is what you get when the rectangles you draw cover a little bit more than the true area under the curve. The lower sum is what you get when your rectangles cover less than the true area under the curve.