Using the Napier's analogy and cosine rule:
$\cos(A-B) = \frac{31}{32}$, $a = 5$, $b = 4$
After applying the formula and solving: $c = 6$
Back to JEE Main 2024 Trigonometry
JEE Main 2024 — Mathematics Trigonometry
medium
mcq
2024
Official previous-year question
Verified 30 May 2026.
Question
In triangle $ABC$, if $a = 5$, $b = 4$, and $\cos(A - B) = \frac{31}{32}$, then $c$ is:
Options
- A
$6$
- B
$7$
- C
$8$
- D
$5$
Solution
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