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Calculating volume.. easy question

by Miike012
Tags: volume
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Miike012
#1
Feb23-12, 12:28 AM
P: 1,011
My work is in the paint doc... my only question is... why is the radi 1-x and not 1+x?

My reason for why I think it is 1 - x is in the paint doc, please let me know why I am wrong.. thank you.
Attached Thumbnails
VOL.jpg  
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Mark44
#2
Feb23-12, 12:33 AM
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Quote Quote by Miike012 View Post
My work is in the paint doc... my only question is... why is the radi 1-x and not 1+x?

My reason for why I think it is 1 - x is in the paint doc, please let me know why I am wrong.. thank you.
Your image is too faint for me to read.
Miike012
#3
Feb23-12, 12:54 AM
P: 1,011
Try this image.
Attached Thumbnails
VOL.jpg  

Mark44
#4
Feb23-12, 12:58 AM
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P: 21,215
Calculating volume.. easy question

Much better - thanks!

The horizontal distance from a point (x, y) on your exponential curve to the line x = 1 is 1 - x. For most of the interval [-1, 0], the x values are negative, so this distance will generally be larger than 1, but less than 2.

Also, the point is labelled incorrectly. It should be (x, f(x)), not (-x, f(-x)).
Miike012
#5
Feb23-12, 01:15 AM
P: 1,011
it should be (x,f(x)) even though its in the 2nd quad? is this general for all quad that x and f(x) be positive when labeling an arbitrary coordinate ?
Mark44
#6
Feb23-12, 11:28 AM
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Quote Quote by Miike012 View Post
it should be (x,f(x)) even though its in the 2nd quad?
Yes.
Quote Quote by Miike012 View Post
is this general for all quad that x and f(x) be positive when labeling an arbitrary coordinate ?
You are assuming that x is always positive and -x is always negative - no, this isn't true. You can't tell the sign of a variable by whether it has a + or - in front of it. For example, -b could be positive or negative, depending on the value of b. Similarly, +c could be positive or negative, depending on the value of c. Note that we don't normally write +c, but I'm just trying to make a point.

Think about the x-axis. If x is a number to the left of zero, it's negative. We DO NOT write this as -x.
Miike012
#7
Feb23-12, 11:48 AM
P: 1,011
Thank you so much that really helps.


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