Find volume of solid rotated about X axis Washer method

In summary, the conversation discusses finding the integral of the function y=x^2+1 within the bounds of x=0 and x=1. The formula needed for this is the integral of PI [f(x)]^2 DX, and the attempt at a solution involved taking the antiderivative of (x^2+1)^2. After some clarification on the meaning of the squared notation, it was determined that the easiest way to integrate the function would be to multiply it out and integrate each term individually. The final solution was found to be 1/3(x^2+1)^3*(1/3x^3+X)^2.
  • #1
2.7taudi
6
0

Homework Statement



y=x^2+1
X in (0,1)

Homework Equations


formula needed
integral (PI [f(x)]^2 DX

in the F(x) just plug in the equation right?

The Attempt at a Solution


took anti deritive of the original problem and came out with

PI[1/3x^3+X]^2
my answer is 5.58

am i on the right track?

im confused on the squared part. Do i take the Anti deritive of the squared or only the thing inside the brackets?
 
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  • #2
Right, you plug f(x) into the formula, but that ^2 means you square f(x), so [f(x)]^2 = (x^2 + 1)^2. That's what you actually want to integrate.
 
  • #3
Bohrok said:
Right, you plug f(x) into the formula, but that ^2 means you square f(x), so [f(x)]^2 = (x^2 + 1)^2. That's what you actually want to integrate.

So how do i take the Anti deritive of that?

is it 1/3(x^2+1)^3*(1/3x^3+X)^2? I am going blank lol should there be a ^2 at the end of that?
 
Last edited:
  • #4
That wouldn't be the way to integrate it

Easiest way would probably be to multiply it out,
(x2+1)2 = (x2+1)(x2+1) = ...
then integrate each term.
 
  • #5
Bohrok said:
That wouldn't be the way to integrate it

Easiest way would probably be to multiply it out,
(x2+1)2 = (x2+1)(x2+1) = ...
then integrate each term.

Got it!

does this look right? excuse my chicken scratch handwriting.
 

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  • #6
Yep, that's it!
 

Related to Find volume of solid rotated about X axis Washer method

1. What is the washer method and how is it used to find the volume of a solid rotated about the x-axis?

The washer method is a mathematical technique used to find the volume of a solid that is created by rotating a two-dimensional region around a horizontal or vertical axis. To use the washer method, you must first determine the boundaries of the region, then integrate along the axis of rotation using the formula V = π∫ab(R(x)^2 - r(x)^2)dx, where R(x) and r(x) represent the outer and inner radii of the washer, respectively.

2. How do you determine the boundaries for the washer method?

The boundaries for the washer method are typically determined by setting the equations of the curves that define the region equal to each other. This creates the points of intersection, which will be used as the boundaries for the integral. The smaller value will be used as the lower limit (a) and the larger value will be used as the upper limit (b).

3. Can the washer method be used for both horizontal and vertical axis of rotation?

Yes, the washer method can be used for both horizontal and vertical axis of rotation. When using the method for a horizontal axis, the outer and inner radii will be functions of y, and the integral will be taken with respect to y instead of x.

4. What are the limitations of using the washer method?

The washer method can only be used for finding the volume of solids that are rotated around a horizontal or vertical axis. It also requires that the boundaries of the region be easily defined and that the outer and inner radii can be expressed as functions of the axis of rotation.

5. Can the washer method be used to find the volume of a solid with a hole in the middle?

Yes, the washer method can be used to find the volume of a solid with a hole in the middle, as long as the boundaries of the region and the outer and inner radii can be determined. The inner radius will be equal to the radius of the hole, and the outer radius will be the distance from the axis of rotation to the outer edge of the solid.

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