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4×5×6+5×6×7+6×7×8+.+150×151×152=?

题目详情
4×5×6+5×6×7+6×7×8+.+150×151×152=?
▼优质解答
答案和解析
考察通项
n*(n+1)*(n+2)
=n*(n+1)*(n+2)[(n+3)-(n-1)]/4
=[n*(n+1)*(n+2)*(n+3)-(n-1)*n*(n+1)*(n+2)]/4
即4×5×6=(4*5*6*7-3*4*5*6)/4
5*6*7=(5*6*7*8-4*5*6*7)/4
.
150*151*152=(150*151*152*153-149*150*151*152)/4
互相抵消
原式=(151*152*153*154-3*4*5*6)/4
=135198666