giúp em bài này với ạ Tính B-A A=1/1.2+1/3.4+1/4.5+……+1/2005/2006 B=1/1008+1/1009+……+1/2006+1/2007 03/10/2021 Bởi Nevaeh giúp em bài này với ạ Tính B-A A=1/1.2+1/3.4+1/4.5+……+1/2005/2006 B=1/1008+1/1009+……+1/2006+1/2007
A=11.2+13.4+...+199.100A=11.2+13.4+…+199.100 =1−12+13−14+...+199−1100=1−12+13−14+…+199−1100 =(1+13+...+199)−(12+14+...+1100)=(1+13+…+199)−(12+14+…+1100) =(1+12+13+...+199+1100)−2(12+14+...+1100)=(1+12+13+…+199+1100)−2(12+14+…+1100) =(1+12+13+14+...+199+1100)−(1+12+...+150)=(1+12+13+14+…+199+1100)−(1+12+…+150) =151+152+...+1100=151+152+…+1100(1) Lại có: BB=201351+201352+...+2013100=201351+201352+…+2013100 =2013(151+152+...+1100)=2013(151+152+…+1100) Bình luận
A=1/1.2+1/2.3+1/3.4+1/4.5+……+1/2005/2006 A=1/1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+……+1/2005-1/2016 A=1-1/2016=2015/2016 B=1/1009+1/1008+1/2007+1/2006 B=(1-1008/1009)+(1-1007/1008)+(1-1006/1007)+(1-1005/1006) B=4-(1008/1009+1007/1008+1006/1007+1005/1006) B=4-1008/1009-1007/1008-1006/1007-1005/1006 B=4-1005/1009=? B-A=?-2015/2016 Bình luận
A=11.2+13.4+...+199.100A=11.2+13.4+…+199.100
=1−12+13−14+...+199−1100=1−12+13−14+…+199−1100
=(1+13+...+199)−(12+14+...+1100)=(1+13+…+199)−(12+14+…+1100)
=(1+12+13+...+199+1100)−2(12+14+...+1100)=(1+12+13+…+199+1100)−2(12+14+…+1100)
=(1+12+13+14+...+199+1100)−(1+12+...+150)=(1+12+13+14+…+199+1100)−(1+12+…+150)
=151+152+...+1100=151+152+…+1100(1)
Lại có:
BB=201351+201352+...+2013100=201351+201352+…+2013100
=2013(151+152+...+1100)=2013(151+152+…+1100)
A=1/1.2+1/2.3+1/3.4+1/4.5+……+1/2005/2006
A=1/1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+……+1/2005-1/2016
A=1-1/2016=2015/2016
B=1/1009+1/1008+1/2007+1/2006
B=(1-1008/1009)+(1-1007/1008)+(1-1006/1007)+(1-1005/1006)
B=4-(1008/1009+1007/1008+1006/1007+1005/1006)
B=4-1008/1009-1007/1008-1006/1007-1005/1006
B=4-1005/1009=?
B-A=?-2015/2016