DEFINITIONS OF MATHEMATICAL FORMS. 293 



as, A C B, Fig. 5. The side opposite the right angle is called 

 the hypothenuse ; as, A B. 



A Parallelogram is a four-sided fig- 

 ure whose opposite sides are parallel ; 

 as, Fig. 6. 



A Rectangle is a parallelogram FtG - 



whose angles are right angles ; as, 

 Fig. 7. 



A Square is a rectangle the sides of which FlG . s. 

 are equal. Fig. 8. A r~ ~] B 



A Trapezoid is a four-sided figure having but 



jj |Q 



two of its sides parallel ; as, A B C D, Fig. 9. 

 The Altitude of a Parallelogram, a 



FIG. 9. 



Rectangle, a Square or a Trapezoid is A ^ B 



the perpendicular distance between ~~7 



the base and the line of the parallel side c E D 



opposite the base ; as, E F, Fig. 9. 



A Circle is a plane surface bounded by a line, every point 

 of which is equally distant from a point called the centre ; 

 as, A B C D, Fig. 10. 



The Circumference of a circle is the line 

 by which it is bounded ; as, A B C D, Fig. 10. 



The Diameter of a circle is a straight line 

 passing through the centre and terminating 

 in the circumference ; as, D E B, Fig. 10. 



The Radius of a circle is the distance from the centre to 

 the circumference ; as, E F. 



