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0_0_38874115_23778.cpp
0_0_38874115_23778.cpp(14) : error C2668: “acos”: 对重载函数的调用不明确
        VC2013\INCLUDE\math.h(1147): 可能是“long double acos(long double) throw()”
        VC2013\INCLUDE\math.h(1031): 或       “float acos(float) throw()”
        VC2013\INCLUDE\math.h(474): 或       “double acos(double)”
        尝试匹配参数列表“(int)”时