CHAPTER III. 

 MEASUREMENT OF AREA. 



4. UNITS OF AEEA. 



i. Area of a square. Draw a square each side of which is one inch 

 long, and also a square with sides two inches long. Divide the latter 

 into four square inches. Then draw a square containing nine square 

 inches. 



Notice that in each of the cases the number of squares is equal to the 

 number obtained by multiplying 

 the length of a side by itself. 



Thus 1x1=1; 



2x2=4; 

 3x3 = 9. 



Multiplying a number by itself 



is called squaring it, and the 



result is known as the square of 



the number. When a small 2 



is written near the top to the 



right of a number in this way, 



6 2 , it means that the square of 

 f the number must be used; in 

 ! fact, the small figure, which is 

 ! called an index, tells you how 

 i many sixes must be multiplied 

 i together; thus, 



6 2 = 6x6 = 36. 



FIG. 9. To illustrate how to divide a square 

 decimetre into square centimetres. 



(6) Draw a square of a deci- 

 metre side and divide two ad- 

 jacent sides into centimetres. Draw lines through the divisions parallel to 

 these sides and count how many square centimetres thus formed there are 

 in a square decimetre. 



(c) Draw a square of any convenient size ; find the number of square 

 centimetres in it. Then measure the length of a side in inches, and calcu- 

 late the number of square inches there are in the figure. 



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