関連ワード:  sec^2 tan^2 identity    sec 2 tan 2 identity    sec 2x tan 2x identity    sec^2 = tan^2 - 1 identity    sec 2 tan 2 trig identity    sec 2x tan 2x trig identity    1 sec 2x tan 2x identity    relationship between sec^2 and tan^2    does sec^2 = tan    tan^2 rule