Realize the tangent function has a period of 180°, so when your calculator (or memory) tells you .. θ = arctan(-1) .. θ = -45° you can translate that value into the desired range by adding multiples of 180° to get the two solutions ... .. θ = 135° .. θ = 315°
The two coordinate pairs for the locations of the other two corners are shaped in rectangle. Two diagonally oposite corners of the park are located ( - 6, 3) and (3, 4)