Question

need answers .. the shortest ones .​

Answer 1

Step-by-step explanation:

(i)

cos²A - sin²A = cosA * cosA - sinA * sinA

                      = cos(A + A)

                   = cos 2A

(ii)

We know that: (1 + cosθ) = 2 cos²(θ/2).

Now,

Given: (1/2)(1 + cosθ)

= (1/2)[2 cos² θ/2]

= cos² (θ/2).

Hope it helps!

Answer 2

cos²A - sin²A

= cosA * cosA - sinA * sinA

= cos(A + A)

= cos 2A