Toán Lớp 6: 1.2+2.3+3.4+…+n(n+1)
1.2.3+2.3.4+3.4.5+4.5.6+…+8.9.10
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Toán Lớp 6: 1.2+2.3+3.4+…+n(n+1)
1.2.3+2.3.4+3.4.5+4.5.6+…+8.9.10
Comments ( 1 )
=1.2.(3-0) + 2.3.(4-1) + … + n.(n+1).[(n+2)-(n-1)]
=[1.2.3+ 2.3.4 + …+ (n-1).n.(n+1)+ n.(n+1)(n+2)] – [0.1.2+ 1.2.3 +…+(n-1).n.(n+1)]
=n.(n+1).(n+2)
=>S=[n.(n+1).(n+2)] /3