一个结晶体的形状为平行六面体，其中，以顶点A为端点的三条棱长都等于1，且它们彼此的夹角都是60°，那么以这个顶点为端点的晶体的对角线的长为______．
如图，
由题意可知，
=AB
=AD
=1，且它们的夹角均为60°，AA1
所以|AC1|=|
+AB
+BC
|=CC1 (
+AB
+BC
)2CC1
=
2+AB
2+BC
2+2(CC1
?AB
+BC
?AB
+CC1
?BC
)CC1
=
=3+2(
+1 2
+1 2
)1 2
．6
故答案为
．6
| 完形填空。 | |||
| May is a 1___________ girl. She 2___________ in China now. She 3___________ two bothers. They are Roy and John. They're eleven. They're in Qi'an Primary School. May 4___________ cooking. She can cook nice food and make nice cakes. Sometimes she likes to make pretty dresses 5___________ her doll. But her brothers 6___________. They like climbing and collecting coins. They 7___________ many different coins. It's a happy 8___________.
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