# Thread: Questions that are driving me crazy cause I can't get the answers that match the book

1. ## Questions that are driving me crazy cause I can't get the answers that match the book

Question 1:
For the graph y= root (9-x)
i) calculate the area of the region bounded by the curve and the coordinate axes in the first quadrant.
ii) calculate the volume of the solid generated when this region is rotated about the x axis.

Question 2:
Sketch the curve x^2=4ay and shade the region bounded by the curve and the Latus rectum y= a. Find the volume of the solid generated when this region is rotated about the axis of symmetry of the parabola.

2. ## Re: Questions that are driving me crazy cause I can't get the answers that match the

Question 1:
For the graph y= root (9-x)
i) calculate the area of the region bounded by the curve and the coordinate axes in the first quadrant.
ii) calculate the volume of the solid generated when this region is rotated about the x axis.

Question 2:
Sketch the curve x^2=4ay and shade the region bounded by the curve and the Latus rectum y= a. Find the volume of the solid generated when this region is rotated about the axis of symmetry of the parabola.

Possibly you have set up the correct integrals but are just making errors in evaluating them. What integrals did you set up?

3. ## Re: Questions that are driving me crazy cause I can't get the answers that match the

This is what I got

https://imgur.com/gallery/JsSiV

4. ## Re: Questions that are driving me crazy cause I can't get the answers that match the

For the latus rectum one, the point S should be (0, a), not (0, 1). Consequently, the integral's limits should be from 0 to a.

5. ## Re: Questions that are driving me crazy cause I can't get the answers that match the

Oh thank you so much

7. ## Re: Questions that are driving me crazy cause I can't get the answers that match the

Are the answers: 27 unit2 and 40.5 pi unit3 ??

8. ## Re: Questions that are driving me crazy cause I can't get the answers that match the

Originally Posted by Drongoski
Are the answers: 27 unit2 and 40.5 pi unit3 ??
No its 18u^2 and 81/2 Pi u^3

9. ## Re: Questions that are driving me crazy cause I can't get the answers that match the

No its 18u^2 and 81/2 Pi u^3
Oh I made a very simple mistake for area - forgot to divide by 3/2. For volume, 40.5 pi is 81/2 pi; just easier to type out.

10. ## Re: Questions that are driving me crazy cause I can't get the answers that match the

Originally Posted by Drongoski
Oh I made a very simple mistake for area - forgot to divide by 3/2. For volume, 40.5 pi is 81/2 pi; just easier to type out.
Can you send me your solutions?

11. ## Re: Questions that are driving me crazy cause I can't get the answers that match the

Can you send me your solutions?
i)
$area = \int ^9 _0 \sqrt{9-x} dx = \left[ -\frac{2}{3} (9-x)^\frac {3}{2} \right ]^9 _0 = 18 unit^2$

ii)
$volume = \pi \int ^9 _0 (\sqrt {9-x})^2 dx = \pi \int ^9 _0 (9-x)dx \\ \\ = \pi \left [ (9x - 0.5x^2)\right]^9 _0
= \frac {81\pi}{2} unit ^3$

Edit: don't know why my part ii) is not displayed?? Can anyone tell me where I went wrong?

12. ## Re: Questions that are driving me crazy cause I can't get the answers that match the

nnn

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