已知|OA|=|a|=3,|OB|=|b|=3,∠AOB=60°,则|a+b|= _ .
问题描述:
已知|
|=|a|=3,|
OA
|=|b|=3,∠AOB=60°,则|
OB
+a
|= ___ . b
答
|
+a
|2=b
2+2a
•a
+b
2b
=9+2|
||a
|cos60°+9=27b
故|
+a
|=3b
3
故答案为3
3