Question

A

2
=
b
2
+
c
2
−
2
b
c
cos
A
Evaluate
cos
A
given that
a
=
8
,
b
=
6
and
c
=
7
.

Answer 1

a^2=b^2+c^2- 2bc cosA

64= 36+ 49 - 2(6)(7)cos A

64- 85 = 84cos A

84 cosA= -21

cos A= -21/84

cosA= -0.25