Question

how do i find the dimensions of a rectangle inside of a semi-cirble?

Answer 1

Hello, how are you doing?

Answer 2

not so good

Answer 3

:/ I am sorry. Shall we try and get rid of this problem then?

Answer 4

yes please

Answer 5

Is there any hint you can give me about your rectangle? So many dimensions can fit into any semi circle. Are the corners touching anything on the circle that you can tell me about?

Answer 6

the flat edge of the semi circle's dimension is 72 and the height or radius of the semi circle is 36. the rectangle fits into the semi circle so that the length of the rectangle is touching the flat edge of the semi circle and two top corners of the rectangle are touching the curve of the semi circle...

Answer 7

Does the rectangle lie on the full 72 length of the semi circle? I'll need more clues I am afraid.

Answer 8

yes, the rectangle does lie on the full 72 length of the semi circle. i forgot how to find the dimensions of inscribed retangles. so long ago and its late

Answer 9

I am sorry, but from the specs you gave me, it is impossible for the rectangle to have anything but 72x0. The top two corners cannot be going up anywhere near 36.

And you are certain this is a rectangle in a semi circle and not the other way around?

Answer 10

If you draw the picture, the circle is possible, but if the rectangle's base is 72, it cannot be inscribed within the semi circle.

Answer 11

yes, i'm certain that this is a rectangle in a semi circle and not the other way around.

problem: you are to design an office block inside a structure witht the following specifications: the building has a rectangular base 150m long and 72m wide. the maximum height of the structure should not exceed 75% of it width for stability or be less than half the width for aesthetic purposes. the maximum height of a room in a public building is 2.5m.

create a model for the curved roof structure when the height is 36m. (i did that)

now, it's telling me to find the dimensions of the cuboid with maximum volume which would fit inside this roof structure

Answer 12

yes, i'm certain that this is a rectangle in a semi circle and not the other way around.

problem: you are to design an office block inside a structure witht the following specifications: the building has a rectangular base 150m long and 72m wide. the maximum height of the structure should not exceed 75% of it width for stability or be less than half the width for aesthetic purposes. the maximum height of a room in a public building is 2.5m.

create a model for the curved roof structure when the height is 36m. (i did that)

now, it's telling me to find the dimensions of the cuboid with maximum volume which would fit inside this roof structure

Answer 13

Right, that's much clearer now. I'll just deal with the second part of the problem.

Answer 14

i know that one of the dimensions of the cuboid will be 150, i'm just having a hard time finding the other two dimensions that happen to be inside the semi circle

Answer 15

Hmm.. This still troubles me because the problem is written so strange. I can't find the connection between the curved roof and the office block.

And if the radius of the semi circle is 36, the biggest length you would be able to build is 72, not 150. I guess I am not understanding the problem clearly here.

Answer 16

this is a three dimensional problem. the office block is shaped like a cube inside the arc-shaped building. i know the cube will be 150m long because that's how long the arc-shaped building is. i'm just having trouble finding the height and width of the cube which can be found on the face of the cube and the face of the cube is touching the face of the arc. when you just look at the front of the building, you will see the semi circle and the rectangle inside the semi circle. i need to know the height and the width of the rectangle if the rectangle's base is fully touching the base of the semi circle and the length of the semi circle is 72m and the height of the semi circle is 36m.

Answer 17

I am trying to dissect this as slowly as I can, sorry for such clueless responses. If it's a cuboid that's 150m, all lengths, widths, and heights are going to be 150m..

Answer 18

well, ok. if its a cuboid all the lengths must be the same. so what would that be because the cube cant fit all the way to the top of the arc-shaped building nor can it stretch all the way equal to the 72 because of the arc...

Answer 19

The max we can do is a cube, and if we are talking angles, that's 45 degrees from the center of the circle, or at 36m.

Answer 20

but 36 doesn't make since because whenever you put a rectangle or square inside a circle or semi circle, there's always gonna be room between the arc and the line of the rectangle/square. therefore, it cant be 36 because that's how high the arc is

Answer 21

Oh no, I meant that the origin is at 36m. If the base is 72m.

Sorry for the absence. Ok. So we know that our radius is 36. So if we go 45 degrees from the center to the circle, that's 36m.

Answer 22

Now we have a triangle with hyp = 36 and angle 45. We can use trig to solve for the other sides.

Answer 23

ok

Answer 24

Let's solve for the adjacent. Know what trig function to use if we have the hyp and need the adj?

Answer 25

cosine

Answer 26

yes, exactly. Can you solve for the adj now?

Answer 27

yeah, i got it

Answer 28

So you got cos(45)*36, correct? =19.911

Answer 29

yeah, i got it

Answer 30

i got 18.911

Answer 31

Oops, Yes, my fault. I was in radians.

Answer 32

lol ok

Answer 33

So we have our x value, and it's equal to our y value. We have a square here.

Answer 34

yup!

Answer 35

If you square that number, you get 648. But that's only for one quarter of our circle. We have 2 quarters in our semi circle so we'll need to double that area for a total max area of 1296.

Answer 36

But that's in 2d, we get to cube 25.456 and then double it for a total of 32,990.773 units cubed.

Answer 37

wait i'm lost. why are we squaring thr 18.9?

Answer 38

uh oh.. You aren't getting 25.456 for cos(45)*36?

Answer 39

nope, i'm in radians and i'm getting 18.9

Answer 40

And we were cubing because if the width value is equal to 25.456, then both altitude and length are also 25.456.

Answer 41

right, that's what i thought, but you said squaring not cubing!

Answer 42

Haha, I am sorry. It is late. I'm also not a pro.

Answer 43

lol ok.
so we cube 18.9

Answer 44

But yes, I'm getting 18.91 too. Sorry.

Answer 45

and then double it.

Answer 46

and why do we double it?

Answer 47

And if the theory works out, that should be the maximum volume for the rectangle inside the arch.

Answer 48

Oh, because we only found one quarter of the full circle, half of the semi circle.

Answer 49

We have two quarters here.

Answer 50

hmmm... ok

Answer 51

hmmm... ok

Answer 52

Does that not make sense?

Answer 53

I wish I could show you all the drawings I did trying to figure this one out lol

Answer 54

If you draw a picture of the semi circle and draw 45 degrees out both ways from the point of origin and then draw the triangles we used to find the length, you will understand why we had to double.

Answer 55

Shoot.. I take it back. You have to quadrupedal. I keep forgetting that we are in 3d.

Answer 56

So double that double.

Answer 57

so co(45)*36 = 18.9. then we cube that because of the three dimensions, then we quadruple that for the volume???

Answer 58

yes, for the total volume.

Answer 59

okay, thank you for all your help!

Answer 60

No problem, so sorry I kept making mistakes. I hope I was somewhat clear in the end.

Answer 61

yeah, enough i guess

Answer 62

But draw a 2d side cutout of it. If you draw lines from the origin, at 36 m going 45 degrees out, you are only accounting for half the semi circle.

Answer 63

ok, i get it

Answer 64

That's why you have to double the volume of one quarter, because a semicircle is really two quarters. And then when you realize that this is a dome, you have to have that depth, so you multiply it by two again.

Answer 65

ok

Answer 66

Great. :D I have to do my math homework now (can't believe this is what I choose to do when I want to procrastinate) and it's 1:30AM, so I will see you later. Have a goodnight!

Answer 67

lol okay! night!