well nice but why not to say immediately 1-cos^2-cos^4 is 1-cos^2(1-cos^2) which is 1-sin^2cos^2 and *4 is 4-sin^2(2a); 2a max can be only 1^2 for 2x45 and (b) 3<=A<=4 is the solution ;) coz [...] Read more