In a rectangular figure the area is equal to width multiplied by length of the rectangle. Expressed in the form of an equation
A = w*l
Where A = area ,
w = width = 6 feet, and
l = length = 9 feet
Therefor:
A = 6*9 = 54 feet^2
If both length and width of the rectangle are increased by a common distance x, the area of the enlarged triangle (A') is given by the following equation.
A' = (w + x)*(l + x) = (6 + x)*(9 + x) = 54 + 15x + x^2
If the increase in area of rectangle is 5 times then:
A' = 5*A = 5*54 = 270 feet^2
Therefor 54 + 15x + x^2 = 270
Therefor: x^2 + 15x - 216 = 0
Therefor: x^2 + 24x - 9x - 216 = 0
Therefor: (x + 24)*(x - 9) = 0
Therefor x = 9 or x = - 24.
We reject the negative value of x. Therefor x = 9.
Thus we will need to add 9 feet to each of width and length of the original rectangle to increase its area 5 times.
Thus the dimensions of expanded rectangle are:
Width = 6 + 9 = 15 feet
Length = 9 +9 = 18 feet
Area = 15*18 = 270 feet^2
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