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Math Help - LRAM and RRAM??

  1. #1
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    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!!
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  2. #2
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    Quote Originally Posted by elpermic View Post
    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.
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  3. #3
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    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???
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  4. #4
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    Quote Originally Posted by elpermic View Post
    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.
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  5. #5
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    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..
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  6. #6
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    Quote Originally Posted by elpermic View Post
    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.
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