The open door policy was challenged by what country with its invasion of manchuria in the 1930s?

The Open Door Policy is a name in foreign affairs preeminent used to stand to the US policy set up in the late nineteenth century and the beginning of twentieth century, as articulated in Secretary of State John Feed's Open Door Note, dated September 6, 1899 and exchange to the significant European forces. 

reflecting point a across the origin negates both of its coordinates.

b = (5, -4)