Question
Question: If in ∆ABC, cos(A – C) cos B + cos 2B = 0 then a<sup>2</sup>, b<sup>2</sup>, c<sup>2</sup> are in-...
If in ∆ABC, cos(A – C) cos B + cos 2B = 0 then a2, b2, c2 are in-
A
A.P.
B
G.P.
C
H.P.
D
None
Answer
A.P.
Explanation
Solution
–cos(A – C) cos(A + C) + 1 – 2sin2B = 0
–[cos2A – sin2C] + 1 – 2sin2B = 0
sin2A + sin2C = 2 sin2B
∴ a2 + c2 = 2b2
a2, b2, c2 are in A.P.