Math, asked by tulasipoorvesh, 2 months ago

cos(n + 1) a.cos(n - 1) a + sin(n + 1) a.
sin(n − 1) a =
1. cos 2n a
2. sin 2na
3. cos 2a
4. sin 2a

Answers

Answered by twinkle385

2

Answer:

Let, A be (n+1)a and B be (n-1)a
Therefore,
CosA .CosB + SinA .Sinb
Cos [A+B] = Cos [ (n+1)a +(n-1)a]
= Cos [ na +a - na +a]
therefore ans is cos2a

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