计算(3a2+2a+1)-(2a2+3a-5)的结果是( )
A:a2-5a+6
B:a2-5a-4
C:a2-a-4
D:a2-a+6
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(I)证明:CD⊥平面PBD;
(II)求二面角A﹣PD﹣C的余弦值.
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涂:____ ____ ____
舒:____ ____ ____
余:____ ____ ____
卡:____ ____ ____