1. 3 rd Year
Quick Questions
8/6/04

2. PERIMETER/AREA FORMULAE - REVISION
1. Rectangle
Area = length ´ breadth
2. Square
3. Triangle

3. Example 1 Find the area of this triangle.

4. 4. Circle
(a) Perimeter
Circumference (C)
C = p x D
p =
Sometimes we use p = 3.14
(rounded to 3 significant figures)

5. Example Calculate the circumference of the following circle.
C = p ´ D
= p ´ 7 =
r = 3.5 cm
= cm (to 3 sig. figs)
D = 7 cm

6. (b). Finding the Area of a Circle
For all circles, the area can be found by using this formula.
Area =   radius  radius
A =  r²

7. EXAMPLES 2.5m 7cm A = r² A = r² = 153.938… = 19.634….. A = 154 cm²
=   7  7
=   2.5  2.5
= …
= …..
A = 154 cm²
A = 19.6 m²

8. A = r² A = r² 6.4m 16cm r = 8cm r = 3.2m = 201.061…. = 32.169….
=  8 8
= 3.2 3.2
= ….
= ….
A = 201cm²
A = 32.2m²

9. MORE EXAMPLES 4.3m A = r² A = r² = 2.4 2.4 = 4.3 4.3 2.4m1.
Area of large circle
Area of small circle
4.3m
A = r²
A = r²
= 2.4 2.4
= 4.3 4.3
2.4m
= …
= ….
A = 58.1m²
A = 18.1m²
Shaded area
= 58.1m² m²
Find the shaded area.
Shaded area= 40m²

10. 24cm Find the shaded area. Square A=2424 = 576cm² 1 circle r =6cm2.
24cm
Find the shaded area.
Square
A=2424
= 576cm²
1 circle
r =6cm
A= r²
=  6 6
A= …
24cm
Area of 4 circles = 4 =
Shaded area = 576cm² - 452cm²
= 452cm²
= 124cm²

11. Find the perimeter and the area of this shape.3.
10cm
Find the perimeter and the area of this shape.
4cm
Area
Perimeter
Circle
Rectangle
C = d
A= r²
A= 4  10
=   10
=   5  5
= 40cm²
= 78.5cm²
= 31.4cm
Perimeter =
Total area =
= 118.5cm²
= 39.4cm

12. area of rectangle – area of semi-circle4.
Find the shaded area.
60cm
40cm
Shaded area
area of rectangle – area of semi-circle
r =30cm
A = 60  40
A= r²  2
= 2400cm²
=  30 30 2
= …
= 1414cm²
Shaded area =
= 986cm²