麻烦写一下化简步骤
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an
= n^2
=n(n+1) -n
=(1/3)[n(n+1)(n+2)-(n-1)n(n+1) ] - (1/2)[ n(n+1) -(n-1)n]
Sn
= a1+a2+...+an
=(1/3)n(n+1)(n+2) - (1/2) n(n+1)
=(1/6)n(n+1)[ 2(n+2) - 3]
=(1/6)n(n+1)( 2n+1)
cn= 8n^2- 4n
Tn
=c1+c2+...+cn
=8[(1/6)n(n+2)( 2n+1)] - 4[ n(n+1)/2]
=(4/3)n(n+1)( 2n+1)] - 2n(n+1)
=(1/3)n(n+1). [ 4(2n+1) - 6 ]
=(1/3)n(n+1). ( 8n-2)
=(2/3)n(n+1). ( 4n-1)
= n^2
=n(n+1) -n
=(1/3)[n(n+1)(n+2)-(n-1)n(n+1) ] - (1/2)[ n(n+1) -(n-1)n]
Sn
= a1+a2+...+an
=(1/3)n(n+1)(n+2) - (1/2) n(n+1)
=(1/6)n(n+1)[ 2(n+2) - 3]
=(1/6)n(n+1)( 2n+1)
cn= 8n^2- 4n
Tn
=c1+c2+...+cn
=8[(1/6)n(n+2)( 2n+1)] - 4[ n(n+1)/2]
=(4/3)n(n+1)( 2n+1)] - 2n(n+1)
=(1/3)n(n+1). [ 4(2n+1) - 6 ]
=(1/3)n(n+1). ( 8n-2)
=(2/3)n(n+1). ( 4n-1)
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