If two lines are perpendicular, then each of the adjacent angles

adjacent angle pair example4
In the figure above, lines l1 and l2 intersect at point O, and they are perpendicular to each other, then four angles are formed, angle1, angle2, angle3 and angle4. For angle1, its adjacent angles are angle2 and angle4. Angle1 and angle2 are an pair of adjacent angles. Angle1 and angle4 are another pair of adjacent angles.
What property does the adjacent angles have?
adjacent angle pair example5
Therefore, The sum of an adjacent angles pair is 180 degrees.
Adjacent angles are equal and each equals to 90 degrees.