= 6/37 nha

đúng 10000000000000000000000000% đó nếu có sai thì trách cái máy tính của mk nha vì k pải mk tính mờ là nó tính....

tk mk nha đg âm 439 kìa....

T_T

lấy máy tính mà tính

bằng 5/31 nha bạn

Ta có : \(A=\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+...+\frac{1}{1147}\)

\(=\frac{1}{1\cdot7}+\frac{1}{7\cdot13}+\frac{1}{13\cdot19}+...+\frac{1}{31\cdot37}\)

\(=\frac{1}{6}\cdot\left(\frac{6}{1\cdot7}+\frac{6}{7\cdot13}+...+\frac{6}{31\cdot37}\right)\)

\(=\frac{1}{6}\cdot\left(1-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+...+\frac{1}{31}-\frac{1}{37}\right)\)

\(=\frac{1}{6}\cdot\left(1-\frac{1}{37}\right)\)

\(=\frac{1}{6}\cdot\frac{36}{37}=\frac{6}{37}\)

Vậy \(A=\frac{6}{37}\)

chắc bạn viết sai đầu bài rồi

A= 6/37

\(=\frac{1}{1.7}+\frac{1}{7.13}+\frac{1}{13.19}+.......+\frac{1}{31.37}=\frac{1-\frac{1}{37}}{6}\)

=1/1×7+1/7×13+1/13×19+...+1/31×37

=1/6×(1-1/7)+1/6×(1/7-1/13)+1/6×(1/13-1/19)+...+1/6×(1/31-1/37)

=1/6×(1-1/7+1/7-1/13+1/13-1/19+...+1/31-1/37)

=1/6×(1-1/37)

=1/6×36/37

=6/37

\(A=\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+...+\frac{1}{1147}\)

\(A=\frac{1}{1.7}+\frac{1}{7.13}+\frac{1}{13.19}+....+\frac{1}{31.37}\)

\(A=\frac{6}{6}\left(\frac{1}{1.7}+\frac{1}{7.13}+\frac{1}{13.19}+...+\frac{1}{31.37}\right)\)

\(A=\frac{1}{6}\left(\frac{6}{1.7}+\frac{6}{7.13}+\frac{6}{13.19}+...+\frac{6}{31.37}\right)\)

\(A=\frac{1}{6}\left(1-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+\frac{1}{13}-\frac{1}{19}+....+\frac{1}{31}-\frac{1}{37}\right)\)

\(A=\frac{1}{6}\left(1-\frac{1}{37}\right)\)

\(A=\frac{1}{6}.\frac{36}{37}=\frac{6}{37}\)

\(A=\frac{1}{6}.\left(\frac{6}{1.7}+\frac{6}{7.13}+\frac{6}{13.19}+...+\frac{6}{31.37}\right)\)

    \(=\frac{1}{6}.\left(1-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+...+\frac{1}{31}-\frac{1}{37}\right)\)

    \(=\frac{1}{6}.\left(1-\frac{1}{37}\right)=\frac{1}{6}.\frac{36}{37}=\frac{6}{37}\)

A = \(\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+...+\frac{1}{1147}\)

A = \(\frac{1}{1.7}+\frac{1}{7.13}+\frac{1}{13.19}+...+\frac{1}{31.37}\)

A = \(\frac{1}{6}.\left(1-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+\frac{1}{13}-\frac{1}{19}+...+\frac{1}{31}-\frac{1}{37}\right)\)

A = \(\frac{1}{6}.\left(1-\frac{1}{37}\right)\)

A = \(\frac{1}{6}.\frac{36}{37}=\frac{6}{37}\)

#)Giải :

\(A=\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{475}+\frac{1}{775}+\frac{1}{1147}\)

\(A=\frac{1}{1.7}+\frac{1}{7.13}+\frac{1}{13.19}+\frac{1}{19.25}+\frac{1}{25.31}+\frac{1}{31.37}\)

\(A=1+\frac{1}{7}-\frac{1}{7}+\frac{1}{13}-\frac{1}{13}+\frac{1}{19}-\frac{1}{19}+\frac{1}{25}-\frac{1}{25}+\frac{1}{31}-\frac{1}{31}+\frac{1}{37}\)

\(A=\frac{1}{7}+\frac{1}{37}\)

\(A=\frac{44}{259}\)

   P/s : Đề bn ghi thiếu nha, còn có 1/475 nữa ( xem đầu phần giải của mình )

      #~Will~be~Pens~#

Câu 3:(x+1).(y-7)=13

Th1:x+1=13

        x=13-1

        x=12

Th2:y-7=13

       y =13+7

       y=20

Vậy x=12 hoặc y=20

a) n + 2 \(\in\)Ư(3) = {1;3}

=> n \(\in\){-1;1}

b) n - 6 \(⋮\)n - 1

=> (n - 1) - 5 \(⋮\)n - 1

=> 5 \(⋮\)n - 1

=> n - 1 \(\in\)Ư(5) = {1;5}

=> n \(\in\){2;6}

1 a,  Ư(3)={-3;-1;1;3}

=> n={-5;-3;-1;1}

b, n-6 chia hết n-1 <=> n-1-5 chia hết n-1<=> 5 chia hết n-1 

               <=> n-1 thuộc Ư(5) ={-5;-1;1;5}

                <=>n ={-4;0;2;6}

A=\(\frac{1}{1.7}+\frac{1}{7.13}+...+\frac{1}{31.37}\)= \(\frac{1}{6}.\)(\(\frac{6}{1.7}+\frac{6}{7.13}+...+\frac{6}{31.37}\))=\(\frac{1}{6}.\)(\(\frac{1}{1}-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+...+\frac{1}{31}-\frac{1}{37}\)) = \(\frac{1}{6}.\left(\frac{1}{1}-\frac{1}{37}\right)=\frac{1}{6}.\frac{36}{37}=\frac{6}{37}\)

ĐS: A=6/37

em làm như sau nhé : :))) 

6A= 6/7 + 6/91+...+ 6/1147

<=>6A= 6/7+1/7-1/13+1/13-1/19+...+1/31-1/37

<=> 6A= 6/7+1/7 -1/37

<=> A=6/37

em không hiểu