in the east of……在一定范围以内的东部,如:
China is in the east of Asian.
to the east of……在一定范围以外的东部,但是不相邻,如：
Japan is to the east of China.
此外还有一个类似的,on the east of……在一定范围以外的东部且紧紧相邻,如：
Korea is on the east of China.