In a triangle ABC, BC = 7, AC = 8, AB = N and = 23. If 49 (3C) + 42 = mn, where (m, n) = 1, then m + n is equal to .
Answer
39
Solution
Cosine rule at A: = 2 + 82 - 722 8 = 23
3 2 - 32 + 45 = 0 ( - 9)(3 - 5) = 0
N = 9
= 72 + 82 - 922 7 8 = 32112 = 27
3C = 4 3C - 3 = 32343 - 67
49 3C + 42 = 327 - 42 + 42 = 327
m + n = 32 + 7 = 39
Answer: 39