1. Our lesson
Area Trapezoids
Confidential

2. Warm Up Find the area: 1. Base = 10 cm, height = 2 cm 10cm2
2. Base = 6 m, height = 4 m m2
Find the base of the triangle:
3. area = 96 cm2, height = 16 cm cm
Find the height of the triangle:
4. Base = 11ft, area = 11 ft ft
5. Base = 12 in, area = 48 in in.
Confidential

3. Let’s review what we have learnt in the last lesson
What is a triangle?
A triangle is a kind of polygon that has three sides.
Examples of triangles:
Confidential

4. Area of a Triangle
The area of a triangle is given by "half of base times height“.
Area =
where b  is the length of the base h  is the height of the triangle.
Note: The height is the length of a line segment perpendicular to the base of the triangle. 1 2
x b x h
Confidential

5. Trapezoid - Introduction
A quadrilateral in which one pair of opposite sides are parallel B A C D
ABCD is a trapezoid in which AB || DC, but AD is not parallel to BC.
Confidential

6. A trapezoid is called an isosceles trapezoid, when its non parallel sides are equal.
A trapezoid is called a right trapezoid, when it has at least two right angles.
Confidential

7. Bases, legs and height of a trapezoidC D E F
The two parallel sides of a trapezoid are called its bases. In the trapezoid ABCD, AB and DC are bases.
The two sides that are not bases are called legs of a trapezoid. AD & BC are the legs of the trapezoid ABCD.
Confidential

8. Bases, legs and height of a trapezoidC D E F G H
A height of a trapezoid is a line segment that is perpendicular to the bases of the trapezoid. DE = BF is the height of the trapezoid ABCD
The median of a trapezoid is the line segment whose endpoints are the midpoints of the legs of the trapezoid. GH is the median of the trapezoid ABCD.
Confidential

9. Area of a trapezoid
To find the area of a trapezoid, consider the following trapezoid ABCD. B A C D F E
Here, DB is the diagonal which divides the trapezoid into two triangles. Now,
Area of trapezoid ABCD = Area of triangle ABD + Area of triangle DBC
= 1/2 * AB * DE + 1/2 * DC * BF
Confidential

10. But, DE = BF which is nothing but the altitude or height ‘ h’
Let, AB = b1 and DC = b2 be the two parallel sides of the trapezoid
Therefore,
Area of trapezoid, A = 1/2 * h (b1 + b2)
Confidential

11. Area of trapezoids
Area of trapezoid, A = 1/2 * h (b1 + b2)
The area of trapezoid is equal to half the product of sum of the parallel sides and the perpendicular distance between them.
Confidential

12. The parallel sides of a trapezoid are 32 cm and 44 cm. If the
Example 1:
The parallel sides of a trapezoid are 32 cm and 44 cm. If the
altitude is 12 cm, find its area.
b1 = 32 cm, b2 = 44 cm, h = 12 cm , A = ?
Area of the trapezoid, A = 1/2 * h (b1+b2)
= 1/2 * 12 (32+44)
= 456 cm²
Confidential

13. Example 2:
The area of a trapezoid is 130 cm²and its bases are 26 cm and 39 cm. Find the height of the trapezoid.
b1 = 26 cm, b2 = 39 cm, A = 130 cm² and h = ?
Area of the trapezoid, A = 1/2 * h (b1+b2)
Height of the trapezoid, h = 2A / (b1+b2)
= (2 * 130) / (26+39)
= 4 cm
Confidential

14. Example 3: The area of a trapezoid of altitude 8 cm is 320 cm².If
one of the parallel sides is 25 cm, find the length of the
other side.
b1 = 25 cm, h = 8 cm, A = 320 cm² and b2 = ?
Area of the trapezoid, A = 1/2 * h (b1+b2)
Length of the base, b2 = (2A /h) – b1
= (2 * 320/8) - 25
= 55 cm
Confidential

15. Your Turn
The parallel sides of a trapezoid are 24 cm & 36 cm and the altitude is 11 cm. Find its area
Answer: 330 cm²
The area of a trapezoid is 360 m². The two parallel sides are 28 m and 12 m. Find the perpendicular distance between the parallel sides.
Answer: 18 m
Find the sum of the lengths of parallel sides of a trapezoid whose area is 0.54 m² and altitude is 9 cm.
Answer: 12 m
The area of a trapezoid of altitude 6 cm is 240 cm². If one of the parallel sides is 45 cm, find the length of the other side.
Answer: 35 cm
Confidential

16. Your Turn
5. The two parallel sides of a trapezoid are 300 cm & 4.5 m. If
its area is 2500 cm², find the perpendicular distance
between the parallel sides.
Answer: 6.67 cm
6. Two parallel sides of a trapezoid are in the ratio 2:5. The
perpendicular distance between them is 9 cm. If the area of
the trapezium is 315 cm², find the sides.
Answer: 20 cm, 50 cm
7. The sum of the parallel sides of a trapezoid is 0.9 m. If the
area of trapezoid is 360 cm², find the perpendicular
distance between the parallel sides.
Answer: 8 cm
Confidential

17. Your Turn The area of a trapezoid is 210 cm²and its height is
14 cm. If one of the bases is longer than the other by
6 cm, find its bases.
Answer: 12 cm, 18 cm
The area of trapezoid is 180 cm²and its height 0.12 m. If one of the parallel sides is half of the other, find the lengths of the two parallel sides.
Answer: 10 cm, 20 cm
The difference of the parallel sides of a trapezoid is 25 cm. If the area of the trapezoid is 240 m²and the altitude is 12 m , find the lengths of its bases.
Answer: 7.5 cm, 32.5 cm
Confidential

18. Refreshment time
Confidential

19. Click on the rabbit to play a game
Confidential

20. other by 4 cm. The perimeter of the trapezoid is 40 cm and the length
1. One of the parallel sides of an isosceles trapezoid is longer than the
other by 4 cm. The perimeter of the trapezoid is 40 cm and the length
of the legs is 8 cm. If the perpendicular distance between
the parallel sides is 6 cm, find the area of the trapezoid and lengths
of all the sides.
h = 6 cm, perimeter = 40 cm
Let b1 = x cm
So, b2 = X+4 cm
Let b3 & b4 be the legs of the trapezoid.
As the trapezoid is isosceles, b3 = b4 = 8 cm
The perimeter of the trapezoid = b1+b2+b3+b4
40 = x+(x+4)+8+8
x = 10 cm
Therefore, the lengths of the parallel sides, b1 = 10 cm & b2 =14 cm
The area of the trapezoid, A = 1/2 h(b1+b2) ; = 1/2 * 6(10+14)
= 72 cm²
Confidential

21. b1 = 2x –1 , b2 = 3x+4, h = 4 cm , Area, A = 127 cm², x = ?
If the area of the following trapezium is 127 cm², find the lengths of the parallel sides.
3x + 4
4 cm
2x-1
b1 = 2x –1 , b2 = 3x+4, h = 4 cm , Area, A = 127 cm², x = ?
The area of the trapezoid = 1/2 h (b1+b2)
127 = 1/2 * 4 [(2x-1)+(3x+4)]
x = 12.4 cm
So, the lengths of the parallel sides, b1 = 23.8 cm, b2 =41.2 cm
Confidential

22. The area of the trapezoid shaped farm, A = 1/2 h(b1+b2)
The trapezoid shaped farm has parallel sides of length 150 m and 250 m. The perpendicular distance between the parallel sides is
35 m. Find the cost of giving manure to the farm at 3.5 $/quintal if, 250 kg of manure have to be fed per hectare.
b1 = 150 m, b2 = 250m, h = 35 m, Area, A = ?
The area of the trapezoid shaped farm, A = 1/2 h(b1+b2)
A = 1/2 (35)( )
A = 7000 m²
1 hectare = m²
For m², the quantity of manure required = 250 kg
For 7000 m², the quantity of manure required = (250/10000)* 7000
= 135 kg
The cost of giving 135 kg of manure to the farm = (3.5/100)* 135
= $ 4.72
Confidential

23. Let’s summarize what we have learnt today
Trapezoid is a quadrilateral in which one pair of opposite sides are parallel.
When the non parallel sides of a trapezoid are equal, the trapezoid is called an isosceles trapezoid.
A right trapezoid is one which has at least two right angles
4. The two parallel sides of a trapezoid are its bases, the two non parallel sides are its legs.
Confidential

24. Let’s summarize what we have learnt today
A line segment that is perpendicular to the bases of the trapezoid is the height of the trapezoid
6. A line segment whose endpoints are the midpoints of the legs of the trapezoid is the median of the trapezoid.
7. The area of the trapezoid is equal to half the
product of its altitude and the sum of its parallel sides.
i.e A = 1/2 * h (b1+b2)
Confidential

25. Do a little more learning each day than you think
You did a great job !
Do a little more learning each day than you think
Confidential