1.

`sum_(r=1)^(n) r^(2)-sum_(r=1)^(n) sum_(r=1)^(n) ` is equal to

Answer» Correct Answer - C
We have,
`underset(r=1)overset(n)sumr^(2)-underset(r=1)overset(n)sumunderset(r=1)overset(m)sumr`
`=underset(r=1)overset(n)sumr^(2)-underset(m=1)overset(n)sum(m(m+1))/(2)`
`=underset(r=1)overset(n)sumr^(2)-(1)/(2)underset(m=1)overset(n)summ^(2)-(1)/(2)underset(m=1)overset(n)summ`
`(1)/(2)underset(r=1)overset(n)sumr^(2)-(1)/(2)underset(r=1)overset(n)sumr=(1)/(2){underset(r=1)overset(n)sumr^(2)-underset(r=1)overset(n)sumr}`


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