=1/4x5+1/5x6+1/6x7+...+1/9x10+1/10x11
=1/4-1/5+1/5-1/6+...+1/10-1/11
=1/4-1/11
=7/44
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Các câu hỏi tương tự
1/6+1/12+1/20+1/30+1/42+...+1/90+1/110
1/6 + 1/12 + 1/20 + 1/30 + 1/42 +.....+ 1/90 + 1/110
B = 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + ...+ 1/90 + 1/110
tính nhanh
1/20+1/30+1/42+1/56+1/72+1/90+1/110+1/132
Tính nhanh:
1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 + 1/110 + 1/132
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/90+1/110 = ?
Tính 1/20 + 1/30 + 1/42 + 1/56 + 1/ 72 + 1/90 + 1/110 + 1/ 132 + 1/156
A = 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 + 1/ 110 + 1/132 + 1/156
Tính nhanh
\(\dfrac{1}{20}\)+\(\dfrac{1}{30}\)+\(\dfrac{1}{42}\)+\(\dfrac{1}{56}\)+\(\dfrac{1}{72}\)+\(\dfrac{1}{90}\)+\(\dfrac{1}{110}\)+\(\dfrac{1}{132}\)
=