# Math Help - Pythagoras' Theorem in geometry question.

1. ## Pythagoras' Theorem in geometry question.

Sophie built a small tower, made of bricks, in her back garden. On top of it she fitted a large glass light-bulb holder.

The diagram shows it as part of a circle.

Centre, C, is 20 centimetres above the top of the wall.

1. Calculate the radius of the circular bulb holder.

2. Use this to find the total height of the structure.

Here's the diagram :

2. ## Re: Please help with this maths question, it's quite easy, I just don't know it. :D

radius of the circle is 20 cm (you really need to have a look at the definition of a radius)

total height = height of the wall + diameter of the circle

3. ## Re: Please help with this maths question, it's quite easy, I just don't know it. :D

Originally Posted by Kyleee
Sophie built a small tower, made of bricks, in her back garden. On top of it she fitted a large glass light-bulb holder.

The diagram shows it as part of a circle.

Centre, C, is 20 centimetres above the top of the wall.

1. Calculate the radius of the circular bulb holder.

2. Use this to find the total height of the structure.

Here's the diagram :
Unless I'm missing something obvious isn't the radius 20cm?

4. ## Re: Please help with this maths question, it's quite easy, I just don't know it. :D

Just to let you guys know : I know what the radius is (half the diameter of a circle), but my teacher said it's an exam question and I'm in the highest maths class. How the heck can it be that easy?

5. ## Re: Please help with this maths question, it's quite easy, I just don't know it. :D

Originally Posted by skeeter
radius of the circle is 20 cm (you really need to have a look at the definition of a radius)

total height = height of the wall + diameter of the circle
I also thought of this too, but I didn't really think this was correct. I think I've did something like this before and I did it like the way you've just said it and I got it wrong. D:

6. ## Re: Please help with this maths question, it's quite easy, I just don't know it. :D

Sorry guys, the diagram is wrong, i'll upload the correct one in a minute.

7. ## Re: Please help with this maths question, it's quite easy, I just don't know it. :D

There! New diagram up; now can you help me?

8. ## Re: Please help with this maths question, it's quite easy, I just don't know it. :D

Originally Posted by Kyleee
There! New diagram up; now can you help me?
one word for you ... Pythagoras.

9. ## Re: Please help with this maths question, it's quite easy, I just don't know it. :D

Skeeter, I know it's pythagoras (that's what my teacher said), but where are the triangles? Please help, I really need to do this. D:

10. ## Re: Please help with this maths question, it's quite easy, I just don't know it. :D

$r^2 = 22^2 + 15^2$

11. ## Re: Please help with this maths question, it's quite easy, I just don't know it. :D

Originally Posted by skeeter
$r^2 = 22^2 + 15^2$
Okay, I know this now, thanks.
But now I need to do question 2 : find the height of the whole thing.

Would I just double the answer and add it to 55? Orrrr...

Edit : Okay, that's totally wrong what I just said. I got muddled up. :P

Would I just do 20 + 55 + ? =

12. ## Re: Please help with this maths question, it's quite easy, I just don't know it. :D

Originally Posted by Kyleee
Okay, I know this now, thanks.
But now I need to do question 2 : find the height of the whole thing.

Would I just double the answer and add it to 55? Orrrr...

Edit : Okay, that's totally wrong what I just said. I got muddled up. :P

Would I just do 20 + 55 + ? =
where did 20 come from?

13. ## Re: Please help with this maths question, it's quite easy, I just don't know it. :D

Well, it's obvious to me that the line shown as 22 is really 20;
that makes radius = sqrt(15^2 + 20^2) = 25.
So height = 55 + 20 + 25 = 100.
All in favor raise your hands !!

14. ## Re: Please help with this maths question, it's quite easy, I just don't know it. :D

the diagram and the wording of the problem are inconsistent. this should be resolved.