2. What is to be learned?
• How to deal with exam type questions
involving compound angles formulas.
3. A
C
B
D
Write the exact value of sin DAB
3
5
LDAB = 90 + x
x
sin DAB = sin (90 + x)
Mark Angle
Write like a formula Cos(A – B ) etc.
Exam Type Question
4. A
C
B
D
3
5
x
sin (90 + x) = sin 90 cos x + cos90 sin x
? ?
sin x = 3
/5
cos x
√ (52
– 32
)
4
= 4
/5
= 1(4
/5) + 0(3
/5)
= 4
/5
Calculate Missing Values
using sin(A + B)
formula
5. 1. Calculate the exact value of Cos DFG
Cos DFG = Cos(x + y)
Cos (x + y) = Cosx Cosy – Sinx Siny
= 1
/√5 X 1
/√10 – 2
/√5 X 3
/√10
= 1
/√50 – 6
/√50
= -5
/√50
= - 1
/
F
D G
E
√10
32
X Y
1
Using Pythag
√5
Key Question
6. x
x
4
3
2. Find the exact value of
a) Sin DAC
b) Cos DAC
3. Find the exact value of
Sin HFT.
A
B
C
D
3√7
/8
1
/8
F
G
H
T
x
5
√21
2
/5
7. x
x
4
3
2. Find the exact value of
a) Sin DAC
b) Cos DAC
3. Find the exact value of
Sin HFT.
A
B
C
D
3√7
/8
1
/8
F
G
H
T
x
5
√21
2
/5
