Finding area bounded Supposedly easy yet I have no clue

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    Area Bounded
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Homework Help Overview

The problem involves approximating the area bounded by the curve f(x) = x² + x, the x-axis, and the line x = 4, using left and right endpoint rectangles. Participants are exploring the method of Riemann sums for this calculation.

Discussion Character

  • Exploratory, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss calculating the area of rectangles and summing them to approximate the total area. There are questions about how to determine the height of the rectangles based on the endpoints used.

Discussion Status

The discussion is ongoing, with some participants sharing their calculations and questioning the differences in results when using left versus right endpoints. Guidance has been offered on the general approach to calculating areas using rectangles.

Contextual Notes

There are indications of confusion regarding the calculations and the relationship between left and right endpoint approximations. Some participants express uncertainty about the initial steps and the method of summing areas.

tjohn101
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Homework Statement


Use the left endpoint graph with the given number of
rectangles to approximate the area bounded by the
curve f (x), the x-axis, and the line x = 4.
f(x)=x2+x

Homework Equations


No idea.


The Attempt at a Solution


Once again, not a clue how to start this.
 

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tjohn101 said:

Homework Statement


Use the left endpoint graph with the given number of
rectangles to approximate the area bounded by the
curve f (x), the x-axis, and the line x = 4.
f(x)=x2+x

Homework Equations


No idea.

The Attempt at a Solution


Once again, not a clue how to start this.

Well, you are calculating the area of each rectangle, and then adding the areas up. You are using 4 rectangles from (0,4). So, you know the length of each rectangle. How do you find the height? Look at where the rectangles touch the graph (i.e., the left endpoint of the rectangle).
 
Okay, I kind of guessed my way through it based on my notes and came up with 88/3 or 29.3333_ . Now, the next question asks me to do the same thing, but use the right endpoint graph. Wouldn't the answers be the same?
 
tjohn101 said:
Okay, I kind of guessed my way through it based on my notes and came up with 88/3 or 29.3333_ . Now, the next question asks me to do the same thing, but use the right endpoint graph. Wouldn't the answers be the same?

You are splitting up the interval (0,4) like this:

(0, 1) (1, 2) (2, 3) (3, 4).

Do you see which are the left and right endpoints?
 
tjohn101 said:
Okay, I kind of guessed my way through it based on my notes and came up with 88/3 or 29.3333_ . Now, the next question asks me to do the same thing, but use the right endpoint graph. Wouldn't the answers be the same?
What did you do to calculate this? I came up with a different answer.
 
So for the left endpoints I just do A=b*h and then add them all up?

Same for the right?
 
tjohn101 said:
So for the left endpoints I just do A=b*h and then add them all up?

Same for the right?
Yep, that's really all there is to a problem of this type. You want to split up the interval, calculate the height at whichever point you're using (left, right, mid), calculate the area of each rectangle, and sum them up.

This all leads into how to calculate the REAL area under the curve, which basically has to do with splitting the interval into infinitely many rectangles!
 
Yeah that's what I'm doing now. That part's okay. Just a little long.
 

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