For any triangle, 



MATHEMATICS 



c : b '.'. a : h 



, ab ce 



n = ?= 



c a 



a : b + e = e : a=h : c 

 b :h ::h :e 



RECTANGLE AND PARALLELOGRAM 



A=ab 



7 



TRAPEZOID 



TRAPEZIUM 



Divide into two triangles and a trapezoid. 

 A = \W + \a(h' 



Or, divide into two triangles by draw- 

 ing a diagonal. Consider the diagonal 

 as the base of both triangles, call its 

 length /; call the altitudes of the triangles hi and h 2 ; then 



ELLIPSE 



8.8 



SECTOR 



/ = length of arc 



'The perimeter of an ellipse cannot be exactly determined without 

 a very elaborate calculation, and this formula is merely an approxima- 

 tion giving fairly close results. 



