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Two rectangular rooms have an area of 240 m? each. The length of one room is x m and the length of the other room is 4 m longer.

(a)
Write down, in terms of x, an expression for the width of each room.
(b)
If the widths of the rooms differ by 3 m, form an equation in x and show that it reduces
to x^2+4x - 320 = 0
(c)
Solve the equation x^2+ 4x - 320 = 0.
(d)
Hence find the difference between the perimeters of the rooms.

1 Answer

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(a) The area of each rectangular room is given by the formula:

Area = length x width

Since the area of each room is 240 m², and the length of one room is x m, we can write:

240 = x × width of the first room

Therefore, the width of the first room is:

width of the first room = 240 / x m

The length of the other room is 4 m longer than x, so we can write:

length of the second room = x + 4 m

And using the formula for the area of the second room, we have:

240 = (x + 4) × width of the second room

Therefore, the width of the second room is:

width of the second room = 240 / (x + 4) m

(b) If the widths of the rooms differ by 3 m, we can write:

width of the second room - width of the first room = 3

Substituting the expressions for the widths obtained in part (a), we get:

240 / (x + 4) - 240 / x = 3

Multiplying both sides by x(x+4), we get:

240x - 240(x + 4) = 3x(x + 4)

Simplifying and rearranging terms, we get:

x^2 + 4x - 320 = 0

(c) To solve the quadratic equation x^2 + 4x - 320 = 0, we can use the quadratic formula:

x = (-b ± sqrt(b^2 - 4ac)) / 2a

where a = 1, b = 4, and c = -320.

Substituting these values, we get:

x = (-4 ± sqrt(4^2 - 4(1)(-320))) / 2(1)

Simplifying the expression under the square root, we get:

x = (-4 ± sqrt(1296)) / 2

x = (-4 ± 36) / 2

Therefore, x = -20 or x = 16.

Since the length of the room cannot be negative, we reject the solution x = -20, and conclude that x = 16 m.

(d) Using the value of x obtained in part (c), we can find the dimensions of each room:

  • The first room has length x = 16 m and width 240 / x ≈ 15 m.
  • The second room has length x + 4 = 20 m and width 240 / (x + 4) ≈ 12 m.

Therefore, the perimeters of the rooms are:

  • Perimeter of the first room = 2(length + width) = 2(16 + 15) = 62 m
  • Perimeter of the second room = 2(length + width) = 2(20 + 12) = 64 m

The difference between the perimeters is:

64 - 62 = 2 m

Therefore, the difference between the perimeters of the rooms is 2 m.


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