SOLUTION: Each side of the squares equals to 7units. How do I calculate the area of an equilateral triangle inside the square with sides 7units? How do I work out the area of a circle

Algebra ->  Surface-area -> SOLUTION: Each side of the squares equals to 7units. How do I calculate the area of an equilateral triangle inside the square with sides 7units? How do I work out the area of a circle       Log On


   



Question 969785: Each side of the squares equals to 7units.
How do I calculate the area of an equilateral triangle inside the square with sides 7units?
How do I work out the area of a circle inside a square with sides equal to 7 units?
What would the ratio be of area of triangle:area of circle?

Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
EQUILATERAL TRIANGLE:
The area of a triangle with sides of lengths a , b , and c ,
opposite angles of measures A , B , and C ,
can be calculated as area=b%2Ac%2Asin%28A%29 :

In the case of an equilateral triangle,
all sides have the same length, b ,
and all angles measure 60%5Eo ,
so area=b%5E2%2Asin%2860%5Eo%29=b%5E2sqrt%283%29%2F2=approximately0.866b%5E2 .

If your equilateral triangle inside a square looks like this ,
then b=s=7 and area=s%5E2%2Asin%2860%5Eo%29=%28sqrt%283%29%2F2%29%2As%5E2=approximately0.866%2As%5E2 .
area=7%5E2%2Asqrt%283%29%2F2=49sqrt%283%29%2F2=approximately0.866%2A49=42.434 .
However, it may not be the expected answer,
but you may be able to fit a slightly larger triangle if you "tilt" it,
like this .

CIRCLE:
The larges circle that you would be able to fit inside a square has a diameter as long as the side of the square:
If the square side length is s, the circle radius is r=s%3F2
The area of a circle of radius r%7D%7D+is+%7B%7B%7Bpi%2Ar%5E2 ,
so a circle of radius s%2F2%7D%7D+would+have+an+area+of%0D%0A%7B%7B%7Barea=pi%2A%28s%2F2%29%5E2=pi%2As%5E2%2F4 .
In particular, for s=7
the area would be area=pi%2A7%5E2%2F4=approximately38.485 .

For the triangle and circle described above,
the ratio of their areas would be
1.103 .
(The side of the square s=7 did not matter, as long as we use the same square size to fit the triangle and the circle).

LARGER TRIANGLE:
In the right triangle corners, according to the Pythagorean theorem,
b%5E2=x%5E2%2Bx%5E2 and b%5E2=%28s-x%29%5E2%2Bs%5E2 , so
x%5E2%2Bx%5E2=%28s-x%29%5E2%2Bs%5E2
x%5E2%2Bx%5E2=s%5E2-2sx%2Bx%5E2%2Bs%5E2
x%5E2=-2sx%2B2s%5E2
x%5E2%2B2sx=2s%5E2
x%5E2%2B2sx%2Bs%5E2=2s%5E2%2Bs%5E2
%28x%2Bs%29%5E2=3s%5E2 , and since x%2Bs%3E0 and s%3E0
x%2Bs=sqrt%283s%5E2%29
x%2Bs=s%2Asqrt%283%29
x=s%281-sqrt%283%29%29 , and x%5E2=s%5E2%281-sqrt%283%29%29%5E2 .
Now, we knew that for a triangle, area=%28sqrt%283%29%2F2%29b%5E2 ,
and that this tilted triangle has b%5E2=x%5E2%2Bx%5E2=2x%5E2 ,
so b%5E2=2%281-sqrt%283%29%29%5E2%2As%5E2 and 0.928s%5E2 .
That makes the area of thte tilted triangle
approximately 0.928%2A7%5E2=45.472 ,
and the ratio of areas for the tilted triangle and circle would be
.
That ratio is approximately 1.182 .