Question

Let cos(α + β) = 4/5 and let sin(α – β) = 5/13, where 0≤α, β ≤ π/4. Then tan2α =
(a) 25/16
(b) 56/33
(c) 19/12
(d) 20/17.

Answer 1

(b) : cos(a + b) = 4/5 giving tan(a + b) = 3/4
Also sin(a – b) = 5/13 given tan(a – b) = 5/12
tan(2α) = tan{(α + β) + (α − β)}