Question

sin (n + 1) A sin (n – 1) A + cos (n + 1) A cos ( n -1) A = cos 2A.​

Answer 1

Answer:

Sorry i didn't understand

Answer 2

Answer:

Here is the proof

Step-by-step explanation:

We know that

$cos(a - b) = sin \:a \: sin \: b \: + cos \: a \: cos \: b$

applying the formula in the equation we get,

$cos(a( n + 1) - a(n - 1))$

taking A common in the equation,

cos(A(n+1-n+1))

=cos(2A)

Hence Proved