Toán Lớp 7: Tính A = 1.4 + 2.5 + 3.6 + 4.7 + … + n(n + 3)
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Toán Lớp 7: Tính A = 1.4 + 2.5 + 3.6 + 4.7 + … + n(n + 3)
Comments ( 2 )
A=4+10+18+21+…+n(n+3)
A có :
(n(n+3)−4/4)+1 (số hạng)
Tổng A là :
A=[n(n+3)+4].[{n(n+3)−4/4}+1]:2
A=(n2+3n+4)[(n2+3n−4/4)+1].1/2
A=n2+3n+4/2.n2+3n/4