Which of the following is true about a

If tan α = 1/2, tan β = 1/3, then find α + β.

If cosα/sinβ =10 and cosα/cosβ =11 then find the value of cos²β=?

If (sinx + siny) = a and (cosx + cosy) = b, then find the value of (sinx siny + cosx cosy).

[A] (a²+b²-2)/ 2

What is the value of (4/3) cot² (p/6) + 3 cos² (150^o) – 4 cosec² 45^o + 8 sin (p/2)?

If cot8A = tan(A+8˚), find the value of A? Given that 8A and A+8 are acute angles.

If 1 + sin 2θ = p² and sin³ θ + cos³ θ = q then Which of the following is true ? 

If (sin 3A sec 6A = 1) , then what will be the value of cos 6A?

In ∆ABC, AB = 5cm, BC = 6cm and AC = 10cm then find out the value of cos A?