Thread: 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 :

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

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?

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?

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:

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

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

Originally Posted by Kyleee

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

one word for you ... Pythagoras.

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:

Originally Posted by skeeter

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 + ? =

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?

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 !!

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