A is in the second quadrant, a∈( 1/4, 1/2)
2a∈( 1/2, 1) three quadrants.
A/2∈( 1/8, 1/4) a quadrant.
2a belongs to two quadrants, namely 2A ∈ (1/4, 1/2) A ∈ (1/8, 1/4).
A/2∑( 1/4, 1/2)A∑( 1/2, 1) three quadrants.