I guess you probably want to use the:
operation instead of the straight divide "/".
Also as a recommendation, break up your expression into smaller pieces for easier debugging. e.g.:
numerator = sec(theta_1).*sec(theta_1).*omega_1;
denominator = (sec(theta_2)).*(sec(theta_2)).*cos(alpha);
answer = numerator ./ denominator;
or even finer pieces.