sum of n terms of series 1²+(1²+2²)+(1+2²+3³)...........
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a = 1 sq. = 1
d = (1 sq. + 2 sq.)- 1sq.
= 1+4 -1
= 5-1
=4
sn= n/2 ( 2a + (n-1)d )
= n/2 (2*1 + (n-1)4 )
= n/2 (2 + 4n - 4 )
= n/2*2( 1 + 2n -2 )
= n ( 2n - 1)
= 2nsq. - n
d = (1 sq. + 2 sq.)- 1sq.
= 1+4 -1
= 5-1
=4
sn= n/2 ( 2a + (n-1)d )
= n/2 (2*1 + (n-1)4 )
= n/2 (2 + 4n - 4 )
= n/2*2( 1 + 2n -2 )
= n ( 2n - 1)
= 2nsq. - n
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