# Thread: surface area of a cone

1. ## 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. ??????

2. Originally Posted by gilzean
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

3. whats the answer????? its a non calculator question

4. Originally Posted by gilzean
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!

5. Originally Posted by mollymcf2009
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

6. Originally Posted by gilzean
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.

7. Originally Posted by gilzean
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.

8. 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

9. Originally Posted by gilzean
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.

10. Originally Posted by gilzean
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.