2 If a = 6, b = 5 and c = 9, then cosA= 7/9
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Answer:
Using cosine rule,
cosA=
2bc
b
2
+c
2
−a
2
cosB=
ac
a
2
+c
2
−b
2
cosC=
2ab
b
2
+a
2
−c
2
we have,
a:b:c=7:8:9
a=7k,b=8k,c=9k
cosA=
2×8k×9k
8k
2
+(9k)
2
−(7k)
2
=
3
2
cosB=
2×7×9
7
2
+9
2
−8
2
=
21
11
cosC=
2×7×8
7
2
+8
2
−9
2
=
7
2
∴cosA:cosB:cosc=14:11:6
Step-by-step explanation:
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