题目内容
△ABC内接于以O为圆心,1为半径的圆,且
+2
-
=
,则
•
的值为( )
OA |
OB |
OC |
0 |
OC |
AB |
A.-1 | B.1 | C.-2 | D.2 |
由题意,|OA|=|OB|=|OC|=1,由
+2
-
=
,可得
=
+2
,
∴平方可得 1=1+4
•
+4,
∴
•
=-1.
∴
•
=(
+2
)•(
-
)=
•
-
2+2
2-2
•
=-1-1+2+2=2,
故选:D.
OA |
OB |
OC |
0 |
OC |
OA |
OB |
∴平方可得 1=1+4
OA |
OB |
∴
OA |
OB |
∴
OC |
AB |
OA |
OB |
OB |
OA |
OA |
OB |
OA |
OB |
OA |
OB |
故选:D.
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