We are given that 1 - 2(sin a)^2 = 2* (cos a)^2 + m. We have to find m.
1 - 2(sin a)^2 = 2* (cos a)^2 + m
=> 1 - 2(sin a)^2 - 2* (cos a)^2 = m
=> 1 - 2[(sin a)^2 + (cos a)^2] = m
now use (sin a)^2 + (cos a)^2 = 1
=> 1 - 2*1 = m
=> 1 - 2 = m
=> m = -1
Therefore m = -1