sin^2 28*+ sin^2 62* + tan^2 38*- cot^2 52*+ 1/4 sec^2 30* = ?

Answer 1

Make use of your "co" factor property.
that is:
sin 28 = cos 62, and tan38 = cot52
note that 28+62 = 90, 38+52=90

sec 30 you must know as part of your trig repertoire