1. STARTERS Find the area of Trapezium = 750 Rectangle = 1000
Half Circle = 628.3
Area =
= cm2

2. Note 6: Finding missing parts of shapes
To find missing sides of shapes, rearrange the formulas .
Example 1: The area of the triangle is 135m2.
Calculate the height of the triangle.
Area = ½  base  height
135 = ½  18  x
135 = 9x
x = 15m

3. Example 2: Calculate the radius of a circle with an area of 65cm2.
Area = π  r2
65 = π  r2
r2 = 65/π
r = √65/π
= 4.5 cm

4. EXERCISES:
Each of these shapes has an area of 60cm2. Calculate the lengths marked x.
10cm
15cm
2.5cm
√60 =7.7cm

5. Calculate the radii of these circles with the given areas.
EXERCISES:
Calculate the radii of these circles with the given areas.
18.7 cm
3.87 m
1.38 cm
0.798 km

6. Radius Diameter circumference EXERCISES:
A circle has an area of 39.47m2. Calculate:
Radius
Diameter
circumference
3.55 m
7.09 m
22.27 m