问题
填空题
已知P为边长为1的等边△ABC所在平面内一点，且满足
|
答案
•PA
=（PB
+PC
）•（CA
+PC
）=CB
2+PC
•（PC
+CB
）+CA
•CB CA
=(
+2CB
)2-（CA
+2CB
）•（CA
+CB
）+CA
•CB
=2CA
2+2CA
•CB
=2+2×1×1×cos60°=3，CA
故答案为 3．
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