Question

The diagram shows 3 identical circles inside a rectangle.

Each circle touches the other two circles and the sides of a rectangle,
as shown in the diagram.
The radius of each circle is 28 mm.
Work out the area of the rectangle.
Give your answer correct to 3 significant figures.

Answer 1

11700 mm²

Explanation:

A rectangle is a quadrilateral with two equal, opposite and parallel sides. Each of the angles in a rectangle is 90°.

The horizontal distance of the rectangle = r + r + r + r = 4r

The vertical distance = r + h + r = 2r + h

Where h is the distance between the midpoint of the 2 up circles and the midpoint of the down circle.

Using Pythagoras:

(2r)² = h² + r²

h² + r² = 4r²

h² = 3r²

h = √3r²

h = r√3

Vertical distance = 2r + h = 2r + r√3

Area of rectangle = vertical distance * horizontal distance

Area = 4r * (2r + r√3) = 8r² + 4r²√3 = 4r²(2 + √3)

Substituting:

Area = 4r²(2 + √3) = 4(28²)(2 + √3) = 11703.711 mm²

Area = 11700 mm² to 3 s.f