函数y=sec2x
导数y'=sec2xtan2xx2=2sec2xtan2x
二阶导数y''=2x(sec2x*2tan2x+sec2x*sec^22x*2)
=2x(2sec2xtan2x+2sec^32x)
=4x(sec2xtan2x+sec^32x)
三阶导数
y'''=4x((2sec2xtan2x+2sec^32x)+3sec^22x*sec2xtan2x*2)
=8x(sec2xtan2x+sec^32x+3sec^32xtan2x)
=8sec2x(tan2x+sec^22x+3sec^22xtan2x)