Given that 1[2]+2[2]+3[2]+...........+9[2]+10[2]
find 1x2+2x3+3x4+..........+10x11
p.s.-[ ]裡面係次方
maths
2007-08-16 3:26 am
回答 (1)
2007-08-16 3:36 am
✔ 最佳答案
1x2+2x3+3x4+..........+10x11=1*(1+1)+2*(2+1)+3*(3+1)+4*(4+1)+...+10*(10+1)
=1[2]+2[2]+3[2]+...........+9[2]+10[2]+1+2+...+10
=1/6*10*11*21+1/2*10*11
=440
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https://hk.answers.yahoo.com/question/index?qid=20070815000051KK04879