note that sec x = 1 cos x so
(1/ cos x) ( 2cos x - sqrt2) = 0
2 - sqrt2 / cos x = 0
2 cos x - - sqrt2 = 0
2 cos x = sqrt2
cos x = sqrt2 / 2
which gives x = pi/4
also as the cos is positive in the 4th quadrant the other value is 7pi / 4
the general solution ( all possible angles) is choice is B.
