A.They studied variations in the appearance of the parent stars. B.They were able to see the planets with a telescope. C.They compared the parent stars to the Sun. D.They sent astronauts on a mission into space.
【简答题】给出下列五个命题: ①函数 y =tan x 的图象关于点( kπ + ,0)( k ∈Z)对称; ②函数 f ( x )=sin| x |是最小正周期为 π 的周期函数; ③函数 y =cos 2 x +sin x 的最小值为-1; ④设 θ 为第二象限的角,则tan >cos ,且sin >cos ; ⑤若 . 其中正确的命题序号是________________________.;