Page 656 - Basic College Mathematics with Early Integers

S E C T I O N 9.2 I PLANE FIGURES AND SOLIDS 633

From the previous example, can you see that in a right triangle, the sum of the
other two acute angles is 90°? This is because
90° + 90° = 180°
c c c
right sum of sum of
angle’s other two angles’
measure angles’ measures
measures

Now we review some special quadrilaterals.A parallelogram is a special quadri-
lateral with opposite sides parallel and equal in length.

A rectangle is a special parallelogram that has four right angles.

A square is a special rectangle that has all four sides equal in length.

A rhombus is a special parallelogram that has all four sides equal in length.

A trapezoid is a quadrilateral with exactly one pair of opposite sides parallel.

parallel
sides

Concept Check True or false? All quadrilaterals are parallelograms. Explain.

In addition to triangles, quadrilaterals, and other polygons, circles are also plane
figures. A circle is a plane figure that consists of all points that are the same fixed
distance from a point c. The point c is called the center of the circle. The radius of a
circle is the distance from the center of the circle to any point on the circle. The
diameter of a circle is the distance across the circle passing through the center.
Notice that the diameter is twice the radius, and the radius is half the diameter.

radius
center
diameter
Concept Check Answer
false