Math

Area And Perimeter Of Trapezium [Explained]

Area of trapezium is the space enclosed in two-dimensional plane geometry and measured in square units. A trapezium is a quadrilateral, which is defined as a shape with four sides (two parallel sides and two non-parallel sides). Thus, the area of a trapezium is the region covered within these four sides.

Properties Of a Trapezium

  • The sum of all the four interior angles of the trapezium is equal to 360° i.e. 180(n-2) = 180(4-2) = 180×2 = 360
  • A trapezium has two parallel sides and two non-parallel sides
  • The length of the mid-segment is equal to half the sum of the parallel bases, in a trapezium
  • The length of both the diagonals is equal.
  • The diagonals of a trapezium always intersect each other.
  • The adjacent interior angles sum up to 180°

Area of Trapezium

The area of a trapezium is the half of multiplication of the height of the trapezium and the sum of the lengths of the two opposite parallel lines. Mathematically,

Area = ½ (a + b) x h

Where h is the height of the trapezium

A is the length of one of the parallel lines

B is the length of the other parallel line

Derivation Of Area of Trapezium

In the diagram below, the trapezium has been divided into three shapes i.e. two triangles and one square.

So, the area will be the sum total of these three shapes i.e. the area of triangle + area of triangle + area of square.

The area of the first triangle is 1/2hx

The area of the second triangle is 1/2hy

The area of the square is a(b-x-y)

Area of trapezium = 1/2hx + 1/2hy + h(b-x-y). Note a = b-x-y, which means x+y = b-a

Area = 1/2h(x+y) + h{b-(x+y)} = 1/2h(b-a) + h(b-b+a) = 1/2h(b-a) + h(a)

Factorize, h(1/2b -1/2a +a) = h(1/2b +1/2a) = 1/2h(b+a) = 1/2*h*(b+a)

Example

Find the area of trapezium in the diagram below

Solution

Area = 1/2*h*(b+a) = 1/2 * 2 * (3+5) = 1/2*2*8 = 8m2

Perimeter of a Trapezium

The perimeter of a trapezium is the sum total of all the four sides of the shape.

Perimeter = |AB| + |BC| + |CD| + |DA|

Read: Examples of supplementary angles

Bolarinwa Olajire

A tutor with demonstrated history of working in the education industry. Skilled in analytical skills. Strong education professional with a M. SC focused in condensed matter.

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