A landowner wishes to use 3 miles of fencing to enclose an isosceles triangular region of as large an area as possible. What should be the lengths of the sides of the triangle? Let x be the length of the base of the triangle. Write the area as a function of x. [First write the length of the equal-length sides in terms of the base, x, then write the height of the triangle in terms of the base.]

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Answer:

The lengths of each side = 1 mile

[tex]A=\frac{x}{4}\sqrt{9-6x}[/tex]

The largest area = 1/4(√3) miles²

Step-by-step explanation:

∵ Th length of the base = x

∵ Perimeter of Δ = 3 miles

∵ The triangle is isosceles

∴ The length of the two equal sides = (3 - x)/2

∵ The height of the Δ is ⊥ to the base and bisect it

∴ h² = [(3 - x)/2]² - (x/2)² = (9 - 6x + x²)/4 - x²/4

∴ h² = 9/4 - 3/2 x + x²/4 - x²/4 = 9/4 - 3/2 x

∴ h = √(9/4 - 3/2 x) = √[(9 - 6x)/4] = 1/2[√(9 - 6x)]

∴ Area of the Δ = (1/2) (x) [1/2√(9 - 6x)]

∴ A = x/4 [√(9 - 6x) ]

∴ [tex]A=\frac{x}{4}\sqrt{9-6x}[/tex]

∵ The largest area of the given perimeter is the area

   of the equilateral triangle

∴ The length of each side = 3/3 = 1 mile

∴ The largest area = 1/4(√3) miles²

The area  is given by half the length of the base times the height, which

gives a length of 1 yard for the base and 1 yard for each equal side.

Response:

  • [tex]Area \ as \ a \ function \ of \ x \ is; = \dfrac{x}{4} \times \sqrt{ {9-6\cdot x}[/tex]
  • The lengths of the sides of the triangle that gives the largest area is 1 yard each

How can the length of the sides that gives the maximum area be found?

The given parameter are;

The shape of the region = Isosceles

The length of the fencing = 3 miles

The length of the base of the triangle = x

Required:

The lengths of the sides of the triangle that gives the maximum area.

Solution:

3 = x + 2·l

Which gives;

[tex]Length \ of \ the \ equal \ sides, \, l = \mathbf{\dfrac{3 - x}{2}}[/tex]

The height of the triangle according to Pythagorean theorem is therefore;

[tex]h^2 = \left( \dfrac{3 - x}{2} \right)^2 - \left(\dfrac{x}{2}\right)^2 = \mathbf{\dfrac{9-6\cdot x}{4}}[/tex]

Which gives;

[tex]Area \ of \ the \ region, \, A = \dfrac{x}{2} \times \sqrt{ \dfrac{9-6\cdot x}{4}} = \dfrac{x}{4} \times \sqrt{ {9-6\cdot x}[/tex][tex]Area \ of \ the \ region, \, A = \dfrac{x}{4} \times \sqrt{ {9-6\cdot x}[/tex]

The area of the region as a function of x is therefore;

[tex]Area \ of \ the \ region, \, A = \dfrac{x}{4} \times \sqrt{ {9-6\cdot x}[/tex]

Therefore;

Maximum or minimum (extremum) area are given as follows;

At the extremum point, we have;

[tex]\dfrac{dA}{dx} = \dfrac{d}{dx} \left(\dfrac{x}{4} \times \sqrt{ {9-6\cdot x}\right) = \mathbf{\dfrac{(3\cdot \sqrt{3} \cdot x - 3\cdot \sqrt{3} )\cdot \sqrt{3-2\cdot x }}{2\cdot x - 12}} = 0[/tex]

Which gives;

3·√3·x = 3·√3

At the maximum point, x = 1

Therefore;

[tex]Length \ of \ the \ equal \ sides, \, l = \dfrac{3 - 1}{2} = 1[/tex]

  • The lengths of the three sides that give maximum area is 1 yard each

Learn more about the maximum value of a function here:

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