As per the question Cos2a + Cos2b = 2
We know that the maximum value of cos x is 1 and the minimum value is -1.
so by taking 1 and -1 value, we can obtain the sum 2.
cos function gives this value at (2n-1)π/2 where sin has value 0 at this place.
so, tan2A.tan2B = sin2A.sin2B / cos2A.cos2B = 0/1 = 0
