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Prove that the rectangle with the largest possible area given a fixed perimeter P is always a square.

Short Answer

Expert verified

The rectangle with the largest possible area given a fixed perimeter P is always a square has been proved.

Step by step solution

01

Step 1. Given information.

We have to prove that the rectangle with the largest possible area given a fixed perimeter P is always a square.

02

Step 2. Find the area.

Let x and y be the sides of the rectangle.

Thus,

P=2x+2y

and,

y=12(P−2x)

The area is :

A=xy=x12(P−2x)

03

Step 3. Derivative of the area.

Derivative of the area is:

A=x12(P−2x)A′=12P−2x=0x=P4

Critical point is x=P4

Since,

A′P4−1>0andA′P4+1<0

So, the first derivative gives us the local maximum at x=P4

Global maximum =0,P2

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