1. anonymous

I'll help with one.

2. anonymous

okay it says to find the volume of the solid

3. anonymous

Do you know the formula for the volume of a cone?

4. anonymous

not of the top of my head

5. anonymous

sorry, my computer just froze up it is (1/3)*Pi*r^2*h

6. anonymous

are 10 and 18 the heights, or are they the length of the lines they are next to?

7. anonymous

yes so $1/3\times \pi \times 5^{2}\times10$

8. anonymous

only if 10 is the height

9. anonymous

$1/3\times \pi \times 5^{2}\times18$

10. anonymous

10 is the height of the top cone and 18 is the height of the bottom cone

11. anonymous

Actually, I don't think so. If you do it that way you get 733.04, which got counted wrong on your test.

12. anonymous

I doubt you would get it wrong for being off by .04

13. anonymous

So, lets assume that 18 and 10 are the lengths of the lines they are next to, and not the heights.

14. anonymous

You following so far?

15. anonymous

yea

16. anonymous

Awesome. We need the heights to use our formula, so now we just need to figure out how to get them. Thinking in 3D is rather tricky, so I like to make this into something I can do in 2D.

17. anonymous

Notice how we have the radius and the hypotenuse of a right triangle?

18. anonymous

ya

19. anonymous

Well, we can use the good old Pythagorean formula to figure out the missing side.

20. anonymous

Sqrt[18^2-5^2] and Sqrt[10^2-5^2] are our two heights

21. anonymous

(1/3)Pi*( Sqrt[18^2-5^2] )^2 + (1/3)Pi*( Sqrt[10^2-5^2] )^2

22. anonymous

^ That should give you the correct answer, which comes out to be...

23. anonymous

idk i dont have a calculator

24. anonymous

oops, I did that formula wrong :/

25. anonymous

(1/3)Pi*( Sqrt[18^2-5^2] )^2 + (1/3)Pi*( Sqrt[10^2-5^2] )^2 isn't right, but you get the idea

26. anonymous

27. anonymous

You get it though, right?

28. anonymous

kinda

29. anonymous

(1/3)*Pi*r^2*h

30. anonymous

you did it right, if 10 and 18 had been the height. Unfortunatly, they were the side length (confusing problem)

31. anonymous

you just use the Pythagorean formula to get the heights, and do the same thing with them that you did with 10 and 18 the first time around.

32. anonymous

Well, I'm sleepy, so I'm off to bed. I have to wake up and do calculus D: