Some patterns of shaded and unshaded small squares is shown. The unshaded squares are those which lie on the diagonals of the figure. By considering the number patterns,
- find the total number of squares in Figure 20,
- find the total number of shaded squares in Figure 43.
- what will be the figure number that will have 144 squares?
Pattern for number of squares
Figure 1: (1 x 2 - 1)
2 = 1
Figure 2: (2 x 2 - 1)
2 = 9
Figure 3: (3 x 2 - 1)
2 = 25
Figure 4: (4 x 2 - 1)
2 = 49
Number of squares = (Figure number x 2 - 1)
2Number of squares for Figure 20
= (20 x 2 - 1)
2 = 39 x 39
= 1521
(b)
Pattern for the number of shaded squares
Figure 1: ((1 - 1) x 2)
2 = 0
Figure 2: ((2 - 1) x 2)
2 = 4
Figure 3: ((3 - 1) x 2)
2 = 16
Figure 4: ((4 - 1) x 2)
2 = 36
Number of shaded squares = ((Figure number - 1) x 2)
2 Number of shaded squares for Figure 43
= ((43 - 1) x 2)
2 = 84 x 84
= 7056
(c)
Number of squares = (Figure number x 2 - 1)
2 Figure number = {(√ Number of squares) + 1} ÷ 2
Figure number with 144 squares
= {(√144 + 1) ÷ 2
= (12 + 1) ÷ 2
= 13 ÷ 2
= 6.5
Answer(s): (a) 1521; (b) 7056; (c) 6.5