Question #315079

A piece of string whose length is 32cm is cut into 2 pieces. one piece is used to form an equilateral triangle and the other to form of the circle so that the sum of the areas is a minimum? Find the minimum sum of the areas. Express your answer in pi. What is the function









Computation of derivative









Computation of Critical numbers









Computation of minimum value










1
Expert's answer
2022-03-21T06:43:36-0400

Solution.

Determine:

x cm - a piece is used to form an equilateral triangle.

32-x cm - a piece is used to form a circle.

S1=a234S_1=\frac{a^2\sqrt 3}{4} - the area of the triangle.

a=x3a=\frac x3 ; S1=x2336S_1=\frac{x^2\sqrt 3}{36}.

S2=πr2S_2=\pi r^2 - the area of the circle.

l=2πrl=2\pi r ; r=l2π=32x2πr=\frac {l}{2\pi}=\frac{32-x}{2\pi};

S2=π(32x2π)2=14π(32x)2S_2=\pi (\frac{32-x}{2\pi})^2=\frac {1}{4\pi}(32-x)^2.

The sum of the areas:

S=S1+S2=x2336+14π(32x)2S=S_1+S_2= \frac{x^2\sqrt 3}{36}+ \frac {1}{4\pi}(32-x)^2 .

Derivative of the function:

S=2x33632x2π=0S’=\frac{2x\sqrt 3}{36}-\frac{32-x}{2\pi}=0

2x336=32x2π\frac{2x\sqrt 3}{36}=\frac{32-x}{2\pi}

x39=32xπ\frac{ x\sqrt 3}{9}=\frac{32-x}{\pi}

x0=932π3+9x_0=\frac{9\cdot32}{\pi\sqrt 3+9} - critical number.

As S’’=318+12π>0S’’=\frac {\sqrt 3}{18}+\frac {1}{2\pi}>0 so S(x0)S(x_0) is the minimum value of the function S(x)S(x).

S(x0)=(932π3+9)2336+14π(32(932π3+9)2)2=S(x_0)=(\frac{9\cdot 32}{\pi\sqrt 3+9})^2\cdot\frac{\sqrt 3}{36}+\frac{1}{4\pi}(32-(\frac{9\cdot 32}{\pi\sqrt 3+9})^2)^2=

256π+33\frac{256}{\pi+3\sqrt 3}

Answer: Smin=256π+33S_{min}= \frac{256}{\pi+3\sqrt 3} cm2cm^2 .


Need a fast expert's response?

Submit order

and get a quick answer at the best price

for any assignment or question with DETAILED EXPLANATIONS!

Comments

No comments. Be the first!
LATEST TUTORIALS
APPROVED BY CLIENTS