(i) Draw the parallelogram shown in Diagram 1 above, of width 6 cm and height 5 cm, on gridded paper and cut it out.
(ii) Draw a line from the top left vertex of the parallelogram straight down, forming a right-angled triangle (line marked in red on Diagram 1).
(iii) Cut along this line and move the triangle from the left side to the right, as shown in Diagram 2. (iv) What new shape have you made? Can you fi nd its area? (v) What have you discovered about fi nding the area of a parallelogram?
Parallelogram a Base (b) Worked example 2
Find (i) the area and (ii) the perimeter of the parallelogram shown.
Solution (ii) 7 cm 15 cm 5 cm b Perimeter = a + b + a + b = 2(a) + 2(b)
Area = base × perpendicular height A = b × ⊥h
6 cm
Practice questions 17.1
1. Suggest an appropriate unit of length that should be used to measure the following. (i) The length of a pencil
(ii) The height of a person
(i) The height of your classroom’s door
(iii) The distance you walk to school
(iv) The width of a human hair
2. Estimate the length of the following, using the correct units, then check to see how close your answer was. (iii) The height of this Maths book
(ii) The width of your desk
(iv) The dimensions of your classroom
(v) The width of your pencil case (vi) The thickness of a €2 coin
3. Sonia runs 9·2 km, while Michelle walks 4 500 metres. How much farther did Sonia run than Michelle walked?
Section B Moving forward 267
(v) The distance from Dublin to Donegal (vi) The length of a spider’s leg