Find the sum of the following :1 + 1 + 1 + 1 + 1 + 1 + 1

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Find the sum of the following :
1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
9 6 12 20 30 42 56 72

=	1	+	1	+	1	+	1	+	1	+	1	+	1	+	1
	9		6		12		20		30		42		56		72

=	1	+	1	+	1	+	1	+	1	+ .....	1
	9		2 × 3		3 × 4		4 × 5		5 × 6		8 × 9

=	1	+	1	−	1	+	1	−	1	+ ... +	1	−	1	=	1
	9		2		3		3		4		8		9		2

Second Method :

1	+	1	+	1	+	1	+	1	+	1	+	1	+	1
9		6		12		20		30		42		56		72

2 × 3

3 × 4

4 × 5

5 × 6

6 × 7

7 × 8

8 × 9

=	1	+		1	−	1
	9			2		(2 + 7)

∵ n = 2 and r = 7

=	1	+	1	−	1	=	1
	9		2		9		2