This is a picture of a chair in my kitchen. The cross in the back was put their for decoration, comfort, and support. If there was no cross in the back the chair would not look very good, your back would not feel as comfortable, and the wood would not be as sturdy. Line A and B are perpendicular to each other. Since they are perpendicular to each other they form right angle. Angle C and angle D are both right angles so they have a measure of 90 degrees. Supplementary angles equal 180 degrees when combined; angle C and angle D are supplementary. Angle C and angle D do not form a linear pair because they are not adjacent to each other.
