ý b bằng 100/501

ý c bằng 100/101

Giải rõ ra chứ

Tính :

a) \(M=\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{99.101}\)

\(=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{99}-\frac{1}{101}\)

\(=1-\frac{1}{101}\)

\(=\frac{100}{101}\)

b) \(A=\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}+...+\frac{7}{69.70}\)

\(=7.\left(\frac{1}{10.11}+\frac{1}{11.12}+\frac{1}{12.13}+...+\frac{1}{69.70}\right)\)

\(=7.\left(\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+\frac{1}{12}-\frac{1}{13}+...+\frac{1}{69}-\frac{1}{70}\right)\)

\(=7.\left(\frac{1}{10}-\frac{1}{70}\right)\)

\(=7.\frac{3}{35}\)

\(=\frac{3}{5}\)

c) \(B=\frac{1}{25.27}+\frac{1}{27.29}+\frac{1}{29.31}+...+\frac{1}{73.75}\)

\(=\frac{1}{2}.\left(\frac{2}{25.27}+\frac{2}{27.29}+\frac{2}{29.31}+...+\frac{2}{73.75}\right)\)

\(=\frac{1}{2}.\left(\frac{1}{25}-\frac{1}{27}+\frac{1}{27}-\frac{1}{29}+\frac{1}{29}-\frac{1}{31}+...+\frac{1}{73}-\frac{1}{75}\right)\)

\(=\frac{1}{2}.\left(\frac{1}{25}-\frac{1}{75}\right)\)

\(=\frac{1}{2}.\frac{2}{75}\)

\(=\frac{1}{75}\)

thanks

M=2/1.3+2/3.5+2/5.7+...+2/99.101

    =1-1/3+1/3-1/5+1/5-1/7+...+1/99-1/101

    =1-1/101

    =101/101-1/101

 M = 99/101

A=7/10.11+7/11.12+7/12+13+7/69/70 ( sai đề )

 B= 1/25.27+1/27.29+1/29.31+...+1/73.75

   =1/2.(2/25.27+2/27.29+2/29.31+...+2/73.75

   =1/2.(1/25-1/27+1/27-1/29+1/29-1/31+...+1/73-1/75

   =1/2.(1/25-1/75)

   =1/2.75/100

   =3/8

thôi chịu nhiều quá ai mà làm đc tự đi mà làm hỏi thì hỏi thì hỏi ít thôi người ta còn trả lời đc .

làm đi mà

làm xong mình cho 1000

ai gia dc jup mk cho 3

1)  a ,  = -a.b-(-a).c+(-a).d

 b, =(a+b).1+(a+b).x+(a+b).y

  = a+b+a.x+b.x+a.y+b.y

c,=(a-b).a+(a-b).b-(a-b).c

=a.a-b.a+a.b-b.b+a.c-b.c