why we subtracted the curve from 4 ?

because when you sketch the cone-type solid using the region by rotating it around x=4,that x=4 line acts like a center line.So,when you sketch a horizontal washer,the center of it is x=4.Therefore,the radius is the region from the center to the curve,aka [4 - (outer curve)] and [4 - (inner curve) ]

Is it always like (4 - outer curve)] and [4 - (inner curve) ]? Can it be (outer curve) - 4 and (inner curve - 4) ? When does each situation occur?

x= 4 is considered your outer curve in that scenario. It's considered the outer curve because it is the furthest function to the right, where as x=y and x= y^2/4 are further to the left making them the smaller function. Therefore it has to be, A= (4-y^2/4)^2-(4-y)^2. Does that kind of help/explain it?

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Calculus, all content (2017 edition)

Course: Calculus, all content (2017 edition) > Unit 6

Lesson 10: Washer method

Washer method worksheet

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Gain some risk-free experience with applying the washer method in this worksheet, before you attempt our exercise.

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Minagtg
Posted 7 years ago. Direct link to Minagtg's post “why we subtracted the cur...”
why we subtracted the curve from 4 ?
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(2 votes)
Answer
- Megh
  Posted 7 years ago. Direct link to Megh's post “because when you sketch t...”
  because when you sketch the cone-type solid using the region by rotating it around x=4,that x=4 line acts like a center line.So,when you sketch a horizontal washer,the center of it is x=4.Therefore,the radius is the region from the center to the curve,aka [4 - (outer curve)] and [4 - (inner curve) ]
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  (9 votes)
Helix8
Posted 7 years ago. Direct link to Helix8's post “Is it always like (4 - ou...”
Is it always like (4 - outer curve)] and [4 - (inner curve) ]? Can it be (outer curve) - 4 and (inner curve - 4) ? When does each situation occur?
Button navigates to signup pageButton navigates to signup page
(2 votes)
Answer
- snsebastian98
  Posted 7 years ago. Direct link to snsebastian98's post “x= 4 is considered your o...”
  x= 4 is considered your outer curve in that scenario. It's considered the outer curve because it is the furthest function to the right, where as x=y and x= y^2/4 are further to the left making them the smaller function. Therefore it has to be, A= (4-y^2/4)^2-(4-y)^2. Does that kind of help/explain it?
  Comment on snsebastian98's post “x= 4 is considered your o...”
  (2 votes)
LynxDLL
Posted 6 years ago. Direct link to LynxDLL's post “For problem 4, how do you...”
For problem 4, how do you graph y^2 = 4x? Thanks
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- cossine
  Posted 6 years ago. Direct link to cossine's post “y^2=4x imply y=+/-2x for ...”
  y^2=4x imply y=+/-2x for x more than or equal zero since you cannot take the square rot of negative number without it being imaginary. Just remember to take the =/- when square rooting for similar function where the function is more than equal to zero
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Tedy Rose Geriane Salutin
Posted 7 years ago. Direct link to Tedy Rose Geriane Salutin's post “what is the diffeence of ...”
what is the diffeence of washer from disk?
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- Specman
  Posted 6 years ago. Direct link to Specman's post “You are subtracting the h...”
  You are subtracting the hole in the doughnut.
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  (1 vote)

Calculus, all content (2017 edition)

Course: Calculus, all content (2017 edition) > Unit 6

Washer method worksheet

Problem 1

Problem 2

Problem 3

Problem 4

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