Results 1 to 7 of 7

Math Help - Volume and surface area question??

  1. #1
    Junior Member
    Joined
    Sep 2008
    Posts
    61

    Volume and surface area question??

    "The lateral edges of a regular hexagonal pyramid are all 20 cm long, and the base edges are all 16 cm long. To the nearest cc, whta is the volume of this pyramid? To the nearest square cm, what is the combined area of the base and six lateral faces?"

    For the volume, I was very confused. I tried to take one third of the base and multiplied it by the height, but I don't know if that is only for regular pyramids. I got 3200 but I don't know if I'm right because I tried it again and I got a diff answer? I haven't done the surface area yet but I'm just so confused, could someone explain to me how this is done.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member 11rdc11's Avatar
    Joined
    Jul 2007
    From
    New Orleans
    Posts
    894
    What do you mean by lateral edges, is that the sides that slant up to form a point on the pyramid?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Sep 2008
    Posts
    61
    Quote Originally Posted by 11rdc11 View Post
    What do you mean by lateral edges?
    Slant height.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Super Member 11rdc11's Avatar
    Joined
    Jul 2007
    From
    New Orleans
    Posts
    894
    Ok I'm not sure if this is right but you would have to find you center point in your base and then use pythrageon theorem to figure out your height since you know a lateral edge.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Super Member 11rdc11's Avatar
    Joined
    Jul 2007
    From
    New Orleans
    Posts
    894
    Ok just wondering by lateral edge you mean the lateral edge is side A of the triangle or is the lateral side if I bisect the triangle at the midpoint of side B?





    1
    101
    10001
    a 1000001 a
    100000001
    10000000001

    b
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Super Member 11rdc11's Avatar
    Joined
    Jul 2007
    From
    New Orleans
    Posts
    894
    So im going to say 20^2= 16^2 + h^2

    so

    h = 12

    B is equal to 384\sqrt{3}

    So now \frac{1}{3}(b)(h)

    That should be your volume which I get it to be 2660cm^3
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Member
    Joined
    May 2008
    Posts
    77
    slant height (or edge length) can be found:
    s^2=h^2+a^2
    where s=slant height, h=height and a=base length.
    It's easy enought to rearrange the formula to get height = 12cm.
    so now you've got:
    base side = 16
    slant height = 20
    height = 12

    Volume is

    and Surface area
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Surface area and Volume
    Posted in the Calculus Forum
    Replies: 5
    Last Post: August 27th 2011, 12:49 PM
  2. box volume/surface area
    Posted in the Geometry Forum
    Replies: 5
    Last Post: December 2nd 2010, 06:53 AM
  3. Surface area and volume?
    Posted in the Calculus Forum
    Replies: 8
    Last Post: October 22nd 2009, 03:14 PM
  4. surface area and volume
    Posted in the Geometry Forum
    Replies: 2
    Last Post: October 19th 2008, 10:56 PM
  5. Volume, Surface Area, and Lateral Surface Area
    Posted in the Geometry Forum
    Replies: 1
    Last Post: April 14th 2008, 11:40 PM

Search Tags


/mathhelpforum @mathhelpforum