Greenwood press

92
QUADRATIC FUNCTIONS
Net of a tin can that is used to deter-
mine the amount of material needed
in manufacturing production.

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QUADRILATERALS
Four-sided plane figures are called quadrilaterals. Quadrilaterals can be con-
vex or concave. The wing structure of the B-117A bomber is in the shape of a
convex quadrilateral (white outline on the illustration below). Special types of
quadrilaterals such as rectangles and squares are used for warning signs and
flags. The illustration shows these common kinds of quadrilaterals: 
• a convex quadrilateral superimposed on the wing structure of a F-117A
Nighthawk;
• a square traffic sign;
• a rectangular flag;
• an isosceles trapezoid superimposed on the bottom section of the John
Hancock Building in Chicago;
• a kite;
• parallelogram faces of a Moissanite-9R CSi crystal structure;
• diamonds (rhombi) on a playing card;
• a city lot in the shape of a trapezoid.
The types of quadrilaterals differ in the number of pairs of parallel sides, size
of angles, and length and direction of diagonals. The parallelogram has parallel
opposite sides. As a result, opposite angles are congruent, and opposite sides are
congruent. If a parallelogram has all four sides of the same length, then it is a
rhombus. This results in the diagonals of a rhombus being perpendicular. A par-
allelogram that has at least one right angle is a rectangle. It must have all right
angles and diagonals that are the same length. A square is simultaneously a rec-