\(\frac{1}{12}\)+\(\frac{1}{20}\)+1/30+1/42+1/56+1/72+1/90+1/110+1/132
=\(\frac{1}{3\cdot4}\)+\(\frac{1}{4.5}\)+1/5x6+1/6x7+1/7x8+1/8x9+...1/11x12
=1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11+1/11-1/12
=1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11+1/11--1/12
=1/3-1/12
=1/4
Xin lỗi bạn nhé!vì trưa rồi nên mình làm vậy cho nhanh thôi!hjhj!
Nếu thấy mình làm đúng thì k mình nha!Thanks các bạn nhìu!
=1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11+1/11+1/12
=1/3-1/12
=4/12-1/12
=3/12
=1/4
=1/4 nhé
các bạn khác chọn (k) đúng cho mình
=1/3*4 + 1/4*5 + 1/5*6 + 1/6*7 + 1/7*8 + 1/8*9 + 1/9*10 + 1/10*11 + 1/11*12
=1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + ... + 1/11 - 1/12
=1/3-1/12
=1/4
= 1 / 3 . 4 + 1 / 4 . 5 + 1 / 5 . 6 + 1 / 6 . 7 + 1 / 7 . 8 + 1 / 9 . 8 + 1 / 9 . 10 + 1 / 10 . 11 + 1 / 11 . 12
= 1 / 3 . 1 / 4 + 1 / 4 . 1 / 5 + 1 / 5 . 1 / 6 + 1 / 6 . 1 / 7 + 1 / 7 . 1 / 8 + 1 / 8 . 1 / 9 + 1 / 9 . 1 / 10 + 1 / 10 . 1 / 11 + 1 / 11 . 1 / 12
= 1 / 3 - 1 / 4 + 1 / 4 - 1 / 5 + 1 / 5 - 1 / 6 + 1 / 6 - 1 / 7 + 1 / 7 - 1 / 8 + 1 / 8 - 1 / 9 + 1 / 9 - 1 / 10 + 1 / 10 - 1 / 11 + 1 /11 - 1 / 12
= 1 / 3 - 1 / 12
= 4 / 12 - 1 / 12 = 3 / 12 = 1 / 4
bạn lập ra \(\frac{1}{12}=\frac{1}{3\cdot4}\)
\(\frac{1}{20}=\frac{1}{4\cdot5}\)
................\(\frac{1}{132}=\frac{1}{11\cdot12}\)
=1/3-1/4+1/4-....+1/11-1/12
=1/3-1/12=3/12=1/4
duyệt nha
\(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}+\frac{1}{132}\)
=\(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+\frac{1}{10.11}+\frac{1}{11.12}\)
=\(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{11}-\frac{1}{12}\)
=\(\frac{1}{3}-\frac{1}{12}\)
=\(\frac{1}{4}\)
1/12= 1/3-1/4
1/3-1/4+1/4-1/5+.............1/11-1/12 =
1/3-1/12= 1/4
