help me out! (1 Viewer)

[HSCExposed]

Need help for a couple questions:

Calculate the volume when the region bounded by the groah y=x^2-4 and the x axis is rotated about the x axis and y axis.

Find the volume of the solid generated when the region in the first quadrant, bounded by the x axis, the line x=8 and the curve y=x^1/3 is rotated about the x axis and the y axis

The line y =x-2 is rotated about the x axis. Find the volume of the solid of revoulition between the planes x=2 and x=3

 

[enigma_1]

Rotated about the x axis and y axis?

Does it want 2 answers?

For the last question to find it, you get y squared which is (x-2)^2
Then to find volume, it's pi times integrate the y squared between x= 2 and x=3.

Sorry if this is useless, on my phone :/

 

[CanU_Not]

Can't use function notation here to save my life orz. Hope this is somewhat good enough for you to understand the basic concepts. (Which is hilarious because I never learnt this properly.)

"The line y =x-2 is rotated about the x axis. Find the volume of the solid of revoulition between the planes x=2 and x=3 " (shortest Q)
1. Graph the function so you can clearly see what area you're trying to find.
2. As you can see by the graph, the region =<2x=<3 is above the x axis. If you rotate that blob about the x axis (try with a sheet of paper) you'll get a circle.
3. You know the formula for the area of a circle is pi* r^2
4. Integrate pi(x-2)^2 with boundaries 2 and 3.
5. Is the answer 1/3pi units squared? If not ignore me lawl.

 

[HSCExposed]

Rotated about the x axis and y axis?

Does it want 2 answers?

For the last question to find it, you get y squared which is (x-2)^2
Then to find volume, it's pi times integrate the y squared between x= 2 and x=3.

Sorry if this is useless, on my phone :/

Yeah its two separate questions, x axis and y axis thanks a lot buddy !

 

[HSCExposed]

Can't use function notation here to save my life orz. Hope this is somewhat good enough for you to understand the basic concepts. (Which is hilarious because I never learnt this properly.)

"The line y =x-2 is rotated about the x axis. Find the volume of the solid of revoulition between the planes x=2 and x=3 " (shortest Q)
1. Graph the function so you can clearly see what area you're trying to find.
2. As you can see by the graph, the region =<2x=<3 is above the x axis. If you rotate that blob about the x axis (try with a sheet of paper) you'll get a circle.
3. You know the formula for the area of a circle is pi* r^2
4. Integrate pi(x-2)^2 with boundaries 2 and 3.
5. Is the answer 1/3pi units squared? If not ignore me lawl.

I got 1/3 and the answer was 1. something, I was like wtf

 

[HSCExposed]

Rotated about the x axis and y axis?

Does it want 2 answers?

For the last question to find it, you get y squared which is (x-2)^2
Then to find volume, it's pi times integrate the y squared between x= 2 and x=3.

Sorry if this is useless, on my phone :/

Done that man got the wrong answer :/

 

[enigma_1]

Yeah its two separate questions, x axis and y axis thanks a lot buddy !

Ohh ok, no probs. If it says find the volume when rotated about the x axis, you integrate y squared

If it says find voluke when it's rotated about y axis, integrate x squared

The formula for volume is V = pi (integrating sign thingy with boundaries) then y squared or x squared depending on the question

It should be in the textbook, have a look over the theory section. Soz once again.

PS I hope you're not using maths in focus :O

 

[enigma_1]

Done that man got the wrong answer :/

Sozzy I have no paper/pen with me atm

 

[enigma_1]

Are you putting the pi at the front? Show me your working