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 angle can be 0 to 2x45 for min&max in sinus :) Well, ok, somebody claims even 3 to 3.25 is solution so (a), but in real school never was. We must see min and max border of solution, not anything in between. So I assume this was not that professional professor..

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