Question

tính A=5/2.4+5/4.6+5/6.8+...+5/98.100

      B=-2/1.2+-2/2.3+-2/3.4+...+-2/2015.2016

 

Answer 1

mình k viết lại đề nhé =)

câu A

A :5 =1/2.4+1/4.6+1/6.8+..+1/98.100

A:5 =1/2-1/4+1/4-1/6+1/6-1/8+...+1/98-1/100

A:5 =1/2-1/100 =49/100

A=49/100 x5 =49/20

câu B tươg tự nha =)

Answer 2

Ta có:

A =5/2(1/2-1/4 + 1/4-1/6+ 1/6..........1/98-1/100)

A =5/2 (1/2 -1/100)

A =5/2 x 49/100

A = 49/20

Answer 3

Xin lỗi: 5/2 x49/100 = 49/40 mới chuẩn

Answer 4

A = \(\frac{5}{2.4}\)+\(\frac{5}{4.6}\)+\(\frac{5}{6.8}\)+ . . . +\(\frac{5}{98.100}\)

A = \(\frac{5}{2}\). \((\frac{2}{2.4}\)+\(\frac{2}{4.6}\)+\(\frac{2}{6.8}\)+ . . . +\(\frac{2}{98.100})\)

A = \(\frac{5}{2}\). \((\frac{1}{2}\)-\(\frac{1}{4}\)+\(\frac{1}{4}\)-\(\frac{1}{6}\)+\(\frac{1}{6}\)-\(\frac{1}{8}\)+ . . . +\(\frac{1}{98}\)-\(\frac{1}{100})\)

A = \(\frac{5}{2}\).\((\frac{1}{2}\)-\(\frac{1}{100})\)

A = \(\frac{5}{2}\).\((\frac{50}{100}\)-\(\frac{1}{100})\)

A = \(\frac{5}{2}\).\(\frac{49}{100}\)

A = \(\frac{245}{200}\)=  \(\frac{49}{40}\)

K CHO MK NHA ! ! !

Answer 5

B = \(\frac{-2}{1.2}\)+\(\frac{-2}{2.3}\)+\(\frac{-2}{3.4}\)+ . . . +\(\frac{-2}{2015.2016}\)

B = \(\frac{-2}{1}-\frac{-2}{2}+\frac{-2}{2}-\frac{-2}{3}+\frac{-2}{3}-\frac{-2}{4}+...+\frac{-2}{2015}-\frac{-2}{2016}\)

B = \(\frac{-2}{1}-\frac{-2}{2016}\)

B = \(\frac{-4032}{2016}-\frac{-2}{2016}\)

B = \(\frac{-4030}{2016}\)

K LUÔN CHO MK NHA ! ! !