Q12Short answer
If cosα + cosβ = 0 = sinα + sinβ, then prove that cos 2α + cos 2β = – 2cos (α + β). [Hint: (cosα + cosβ)2 – (sinα + sinβ)2 = 0] sin ( x + y ) a+b tan x a
If cosα + cosβ = 0 = sinα + sinβ, then prove that cos 2α + cos 2β = – 2cos (α + β). [Hint: (cosα + cosβ)2 – (sinα + sinβ)2 = 0] sin ( x + y ) a+b tan x a