m ( ∡AOB ) + m ( ∡BOC ) = 90° => m ( ∡BOC ) = 90° - 50° = 40° ;
Construim [OE - bisect. ∡AOB => m ( ∡AOE ) = m ( ∡BOE ) = 50 / 2 = 25°
Construim [OF - bisect. ∡BOC => m ( ∡BOF ) = m ( ∡COF ) = 40 / 2 = 20°
m ( ∡EOF ) = m ( ∡EOB ) + m ( ∡BOF ) = 25° + 20° =45°