1. So the large triangle is right-angled.
Reminder - don’t copy
a = (180 – 40)  2
= 70°
b = a = 70° e° c°
40°
c = 180 – 40
= 140° a° d° b°
d = (180 – 140)  2
= 20°
e = d = 20°
NB: b + d =
= 90°
So the large triangle is right-angled.

2. Triangles Inside Semi-Circles
Rule: any triangle drawn inside a semi-circle is right-angled. ie a° b°
a = 90
b = 90

3. Exs Find the missing angles !
35°
25° x° e d c b y°
x = 90
a = 90 – 25 = 65
b = 25
y =
c = 180 – = 130
= 55
d = 180 – 130 = 50
e = a = 65

4. Find (i) diameter (ii) circumferenceEx
Find (i) diameter (ii) circumference
(i) d2 = =
= 676 d
d = 676
= 26
10cm
24cm
Diameter = 26cm
(ii) C = d
= 3.14 X 26
= 81.64
= 81.6cm

5. Find (i) x (ii) area of triangle.Ex
Find (i) x (ii) area of triangle.
(i) r = 8.5 so d = 17 x
8cm
8.5cm x 8 17
x2 = =
= 225
x = 225
= 15cm
(ii) Area = base X height  2
= 8 X 15  2
= 60cm2