Cosine Rule (missing side)
a
2
=
b
2
+
c
2
−
2
b
c
C
o
s
A
Find x (to 2 d.p.)
5
8
x
20°
x
2
=
5
2
+
8
2
−
2
(
5
)
(
8
)
C
o
s
(
20
∘
)
=
25
+
64
−
80
(
0.939
)
=
13.88
⟹
x
=
3.73
(
t
o
2
d
.
p
.
)