已知O为坐标原点,
=(x,y),
=(a,0),
=(0,a),
=(3,4),记|
|、|
|、|
|中的最大值为M,当a取遍一切实数时,M的取值范围是( )
| OP |
| OA |
| OB |
| OC |
| PA |
| PB |
| PC |
A、[
| ||
B、[7+2
| ||
C、[7-2
| ||
D、[7,7+2
|
若数列{an}的通项公式为an=
,其前n项和为
,则n为( )
| 1 |
| n2+3n+2 |
| 7 |
| 18 |
| A、5 | B、6 | C、7 | D、8 |