给出下列四个结论:①函数y=a x (a>0且a≠1)与函数y=log a a x (a>0且a≠1)的定义域相同;②函数y=k3 x (k>0)(k为常数)的图象可由函数y=3 x 的图象经过平移得到;③函数 y= 1 2 + 1 2 x -1 (x≠0)是奇函数且函数 y=x( 1 3 x -1 + 1 2 ) (x≠0)是偶函数;④函数y=cos|x|是周期函数.其中正确结论的序号是 ______.(填写你认为正确的所有结论序号)
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