A wire 20 feet long is to be cut into two pieces. One piece will be shaped as a square and the other piece
will be shaped as an equilateral triangle. Express the total area A enclosed by the pieces of wire as a
function of the length x of a side of the equilateral triangle. What is the domain of A?

Respuesta :

To answer this question we just need to calculate areas of the equilateral triangle and the area of the square:

Solution is:

At = (√3/4)×x²  +  ( 20 - 3×x )²/ 16  square units

for    0 ≤ x  ≤ 6.66   and        18.87 ≤  A ≤ 25

In the equilateral triangle, all the interior angles are 60°.

The bisectrix of one of these angles divided one 60°angle into two 30° angles, and the opposite side in half, and two isosceles triangles are formed.

The area of the original equilateral triangle of side x will become the sum of the areas of the two isosceles triangles with common side ( and height)  h = ( √3 /2)×x

cos 30° = √3  / 2     ⇒  h =  (√3  / 2) ×x

Then as Aet = 2 × (1/2)×(x/2)× (√3  / 2) ×x

Aet = (√3/4)×x²  square units

To obtain the area of the square we know that a square of side L will have an area of L², so we only need to find out what is the side of the square.

The length of the wire is 20 f.

we cut off to get the equilateral triangle 3×x then we got left

20 - 3×x so the perimeter of the square is

p = 20 - 3×x  

In the case of square p = 4×L     then  L = p/4

L = ( 20 -3×x)/4

As= [ ( 20- 3×x)/4]²   ⇒   As = ( 20 - 3×x )²/ 16  square units

Finally total area

At = (√3/4)×x²  +  ( 20 - 3×x )²/ 16  square units

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Universidad de Mexico