Answer:
Length = 7 ft
Breadth = 7 ft
Step-by-step explanation:
Let lenght of rectangle be x
and breadth be y
Area = [tex]49\ \text{ft}^2[/tex]
[tex]xy=49\\\Rightarrow x=\dfrac{49}{y}[/tex]
Permiter of a rectangle is given by
[tex]P=2(x+y)\\\Rightarrow P=2x+2y\\\Rightarrow P=2\times\dfrac{49}{y}+2y\\\Rightarrow P=\dfrac{98}{y}+2y[/tex]
Differentiating with respect to y we get
[tex]\dfrac{dP}{dy}=-\dfrac{98}{y^2}+2[/tex]
Equating with zero
[tex]0=-\dfrac{98}{y^2}+2\\\Rightarrow -2=-\dfrac{98}{y^2}\\\Rightarrow y^2=\dfrac{98}{2}\\\Rightarrow y^2=49\\\Rightarrow y=7[/tex]
Double derivative of the equation
[tex]\dfrac{d^2P}{dy^2}=2\dfrac{98}{y^3}\\\Rightarrow \dfrac{d^2P}{dy^2}=\dfrac{196}{y^3}>0[/tex]
So the value of y is minimum at 7.
[tex]x=\dfrac{49}{y}=\dfrac{49}{7}\\\Rightarrow x=7[/tex]
Hence, [tex]x=7,y=7[/tex]
The mimimum length and breadth of the rectangle is both 7 ft.
