I'm stuck again! (1 Viewer)

[Yoko Hono]

With a question like this:

The region bounded by the curve y=x^2 - 5x and the x axis is rotated about the x axis. Find the volume of the solid generated.

how do you find out what a and b are for the formula
V = pie b y^2 dx
............ S
............ a

?

And what is the answer to this question? I keep getting 104.17 ( to 2 dp) but the answer in the book is 327.25

 

[nick1048]

dude are u multiplying 104.17 by pi... it turns out correct.

 

[Yoko Hono]

I am sooo stupid. I can't believe i missed that. But do you know how to find a and b from the question?

 

[nick1048]

dude are u multiplying 104.17 by pi... it turns out correct.

here is the working

lol sorry about the shotty handwriting. You get a and b from solving the quadratic equation i.e. when y = 0 what does x = ? please check the attachment thankyou.

 

[Yoko Hono]

Thanks heaps for that - it makes sense now.