Help with Surface Area and Volume of Figures!

[isu23pink]

i re-did the Volume for #1 2x already and i keep getting it wrong, this is what i did:
V=(1/2)(4)(3.5)(12)= 84in^3

for #4 i did:
x=rad28 = 2rad7
LA = (1/2)(48)(8)
= (1/2)384
= 192 + B
= 192 + 144
= 336

and for the volume i did:
V = (1/3)(2rad7)(336)
= (1/3)(672rad7)
= 224rad7

for #5, the volume part i did:
V= (1/3)(42pi)(5)
= (1/2)(210pi)
= 70pi

and for #8 i did v= pi1.5^2
= 2.25(h)
= 6.75(3)
= 20.25

i need help please.

 

[Deleted member 4993]

i re-did the Volume for #1 2x already and i keep getting it wrong, this is what i did:
V=(1/2)(4)(3.5)(12)= 84in^3

for #4 i did:
x=rad28 = 2rad7
LA = (1/2)(48)(8)
= (1/2)384
= 192 + B
= 192 + 144
= 336

and for the volume i did:
V = (1/3)(2rad7)(336)
= (1/3)(672rad7)
= 224rad7

for #5, the volume part i did:
V= (1/3)(42pi)(5)
= (1/2)(210pi)
= 70pi

and for #8 i did v= pi1.5^2
= 2.25(h)
= 6.75(3)
= 20.25

i need help please.

For #1 - your work seems correct - if the height of the triangle is 3.5 in and base = 4"

May be the problem is stating that the slant sides are 3.5"

then

\(\displaystyle Height \, = \, \sqrt{3.5^2 - 2^2} = 2.872281323\)

\(\displaystyle Voume \, = 2 * 2.872281323 * 12 = \, 68.93475175 = 67 in^3\)

 

[Loren]

The volume of a pyrmid is V=(1/3) times the area of the base times the altitude. V=(1/3)(12[sup:3tx1nsh7]2[/sup:3tx1nsh7])(8)

 

[isu23pink]

okay, i get it, thanks. but i still need help on those other problems s

 

[galactus]

#3: The volume of a cone is \(\displaystyle \frac{\pi}{3}r^{2}h\)

But, we are given the slant length, not the height. Use Pythagoras to find h, then plug in your values.

#5 is similar, only the radius is 4

#8. The volume of a sphere with diameter 3 is \(\displaystyle \frac{4}{3}{\pi}(\frac{3}{2})^{3}=\frac{9\pi}{2}\)

There are 3 of them, so multiply that result by 3.

Find the volume of the cylinder with radius 3/2 and height 9. Then, subtract the two values.