...  t sin 2018 t   x sin 2018 x d t  d t   sin2018 t  cos2018 t  sin 2018 x  cos2018 x dx sin 2018   t   cos2018   t  0 2018   x sin 2018 x x sin 2018 x  sin 2018 x d x... dx 2018 2018 2018 2018 2018  sin x  cos x sin x  cos x sin x  cos2018 x 0   Suy I          sin 2018 x   sin 2018 x sin 2018 x  I   dx    dx   dx  2018 2018 sin 2018. .. sin 2018 x  cos 2018 x  sin 2018 x  cos 2018 x sin x  cos x      Đặt x  u  ta suy      sin 2018 x cos2018 u cos2018 x dx   du   dx 2018 2018 2018 2018 2018 sin x  cos x