Answer: He marked angle of depression in the wrong side.
Step-by-step explanation:
Angle of depression : If someone stands and looks down at an object, the angle of depression is the angle between the horizontal line of his sight and the object.
If point O shows the bottom of a house window, A shows the position of ball and OX is the horizonal line.
Then, By the definition of angle of depression,
Angle XOA is the angle of depression from the bottom of a house window to a ball on the ground.
That is, [tex]\angle XOA = 20^{\circ}[/tex]
