Results 1 to 10 of 10

Math Help - surface area of a cone

  1. #1
    Newbie
    Joined
    Feb 2009
    Posts
    21

    surface area of a cone

    the diagram shows a cone.
    the radius of the base of the cone is 10cm
    the slant height of the cone is 15cm

    (a) work out the total surface area of the cone. ??????
    Last edited by gilzean; February 10th 2009 at 09:52 AM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member TheMasterMind's Avatar
    Joined
    Dec 2008
    Posts
    155
    Quote Originally Posted by gilzean View Post
    the diagram shows a cone.
    the radius of the base of the cone is 10cm
    the slant height of the cone is 15cm

    (a) work out the total surface area of the cone. ??????
    The formula for SA of a cone is SA=\pi r s + \pi r^2

    you have r and know the slant height, make a right triangle out of that and use trig ratios to find the height, h and then use the formula
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Feb 2009
    Posts
    21
    whats the answer????? its a non calculator question
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Senior Member mollymcf2009's Avatar
    Joined
    Jan 2009
    From
    Charleston, SC
    Posts
    490
    Awards
    1
    Quote Originally Posted by gilzean View Post
    the diagram shows a cone.
    the radius of the base of the cone is 10cm
    the slant height of the cone is 15cm

    (a) work out the total surface area of the cone. give your answer as a multiple of pie. i got 15x10 = 15- pie(squared)
    IS THAT WRONG?
    IF SO.... what is teh correct answer and what are the workings no compelx stuff pelase just simple workings :
    The area of a cone formula is A = \pi r \sqrt{r^2+h^2} but you would use that if you were given the height of the cone, not the length of the slant side of the cone as in your problem. So you need to find the height of your cone.

    To determine the height of your cone:

    Since you are given the length of the slant side, you need to find the height of the cone itself. A cone is made from a right triangle that is rotate around itself, right? You are given one of the legs of the triangle, it is the radius of your cone. You are also given the length of the hypotenuse (the slant side). Use the Pathagorean theorum (a^2 + b^2 = c^2) to find the height of the triangle which is also the height of your cone. Then you can use the formula for the area of a cone to find your answer.

    Remember that a & b of your Pathagorean equation are the legs, and c is your hypotenuse.

    Does this make sense? Good luck!
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Feb 2009
    Posts
    21
    Quote Originally Posted by mollymcf2009 View Post
    The area of a cone formula is A = \pi r \sqrt{r^2+h^2} but you would use that if you were given the height of the cone, not the length of the slant side of the cone as in your problem. So you need to find the height of your cone.

    To determine the height of your cone:

    Since you are given the length of the slant side, you need to find the height of the cone itself. A cone is made from a right triangle that is rotate around itself, right? You are given one of the legs of the triangle, it is the radius of your cone. You are also given the length of the hypotenuse (the slant side). Use the Pathagorean theorum (a^2 + b^2 = c^2) to find the height of the triangle which is also the height of your cone. Then you can use the formula for the area of a cone to find your answer.

    Remember that a & b of your Pathagorean equation are the legs, and c is your hypotenuse.

    Does this make sense? Good luck!
    i want you to tel lme teh answer of the question
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Senior Member mollymcf2009's Avatar
    Joined
    Jan 2009
    From
    Charleston, SC
    Posts
    490
    Awards
    1
    Quote Originally Posted by gilzean View Post
    i want you to tel lme teh answer of the question
    How does me telling you the answer help you to learn how to do this? This is your homework, not mine. Do the work using the information I gave you. Come back with the work that you have done if you are still having trouble and I will be happy to help you understand it.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Member TheMasterMind's Avatar
    Joined
    Dec 2008
    Posts
    155
    Quote Originally Posted by gilzean View Post
    i want you to tel lme teh answer of the question
    Do the work. You learn math by doing problems yourself! Math is not a spectator sport, you learn it by doing, not by watching others do the problems for you. Make an attempt at the solution and only then will further help be provided.
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Newbie
    Joined
    Feb 2009
    Posts
    21
    telling me a formula for a caculator question and not answering the actual question "what is the totaly surface area" does not help . I'm a simple B grade maths student who needs the answers to these questions and time is seriously running out
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Senior Member mollymcf2009's Avatar
    Joined
    Jan 2009
    From
    Charleston, SC
    Posts
    490
    Awards
    1
    Quote Originally Posted by gilzean View Post
    telling me a formula for a caculator question and not answering the actual question "what is the totaly surface area" does not help . I'm a simple B grade maths student who needs the answers to these questions and time is seriously running out

    This is not a formula for a calculator. This is how you do the problem. It is not our job to answer the question for you. None of us is getting paid to help you. You should thank people that try to help you instead of complaining about the help you have been given.

    This is Math HELP Forum, not Math ANSWERS Forum.
    Follow Math Help Forum on Facebook and Google+

  10. #10
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by gilzean View Post
    the diagram shows a cone.
    the radius of the base of the cone is 10cm
    the slant height of the cone is 15cm

    (a) work out the total surface area of the cone. ??????
    Duplicate question posted here: http://www.mathhelpforum.com/math-he...area-cone.html

    This thread is closed - I can't be bothered trying to merge the two threads into anything semi-coherent.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Surface area of a cone
    Posted in the Geometry Forum
    Replies: 5
    Last Post: November 8th 2011, 06:20 PM
  2. [SOLVED] Lateral surface area of a cone
    Posted in the Geometry Forum
    Replies: 2
    Last Post: March 7th 2011, 10:25 AM
  3. Surface area and inscribed cone
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: July 27th 2010, 03:36 PM
  4. cone/ surface area...
    Posted in the Geometry Forum
    Replies: 2
    Last Post: February 13th 2010, 02:17 AM
  5. Finding the Surface Area of a Cone?
    Posted in the Geometry Forum
    Replies: 1
    Last Post: February 11th 2009, 12:48 PM

Search Tags


/mathhelpforum @mathhelpforum