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Question: Answered & Verified by Expert
In a triangle $A B C$ with usual notations, If $a: b: c=7: 8: 9$ : then $\cos A: \cos B: \cos C=$
MathematicsTrigonometric Ratios & IdentitiesMHT CETMHT CET 2022 (11 Aug Shift 1)
Options:
  • A 14:11:6
  • B 7:8:9
  • C 3:4:5
  • D 5:6:7
Solution:
2620 Upvotes Verified Answer
The correct answer is: 14:11:6
Let $a=7 k, b=8 k, c=9 k$
Using cosine rule $\cos A=\frac{2}{3}, \cos B=\frac{11}{21}, \cos C=\frac{2}{7}$
$Rightarrow \cos A: \cos B: \cos C=14: 11: 6$

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