Question

formula of cos²a- cos²b​

Answer 1

Step-by-step explanation:

cos²a-cos²b

cos²(a-b)

Answer 2

Step-by-step explanation:

Given that

$co {s}^{2} a - co {s}^{2} b = \frac{1}{2} (cos2a - cos2b)$

$co {s}^{2} a = \frac{1}{2} (1 + cos2a)$

$co {s}^{2} b = \frac{1}{2} (1 + cos2b)$

thus,

$co {s}^{2} a - co {s}^{2} b = \frac{1}{2} (1 + cos2a) - \frac{1}{2} (1 + cos2b)$

$= \frac{1}{2} (cos2a - cos2b)$