= \(\frac{4}{99}\)

chuẩn 100%

Hội con 🐄 chúc bạn học tốt!!! 

\(\frac{1}{45}+\frac{1}{105}+\frac{1}{189}+\frac{1}{297}=\frac{4}{99}\)

Học tốt !!!

\(S=\frac{1}{9}+\frac{1}{45}+\frac{1}{105}+\frac{1}{189}+\frac{1}{297}=\frac{1}{3}\left(\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right)\)

\(=\frac{1}{3}.\frac{1}{2}\left(\frac{2}{3}+\frac{2}{15}+\frac{2}{35}+\frac{2}{63}+\frac{2}{99}\right)=\frac{1}{6}\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}\right)\)

\(=\frac{1}{6}\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\right)=\frac{1}{6}\left(1-\frac{1}{11}\right)=\frac{1}{6}.\frac{10}{11}\)

\(=\frac{5}{33}\)

Bài làm:

\(S=\frac{1}{9}+\frac{1}{45}+\frac{1}{105}+\frac{1}{189}+\frac{1}{297}\)

\(S=\frac{1}{6}\left(\frac{2}{3}+\frac{2}{15}+\frac{2}{35}+\frac{2}{63}+\frac{2}{99}\right)\)

\(S=\frac{1}{6}\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}\right)\)

\(S=\frac{1}{6}\left(\frac{3-1}{1.3}+\frac{5-3}{3.5}+\frac{7-5}{5.7}+\frac{9-7}{7.9}+\frac{11-9}{9.11}\right)\)

\(S=\frac{1}{6}\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\right)\)

\(S=\frac{1}{6}\left(1-\frac{1}{11}\right)\)

\(S=\frac{1}{6}.\frac{10}{11}=\frac{5}{33}\)

Vậy \(S=\frac{5}{33}\)

Xin lỗi bạn Xyz nhé, mk ko có chép bài bạn đâu! với lại mk cx ko k sai bài bn đâu nhé!

S = 1/9 + 1/45 + 1/105 + 1/189 + 1/297

=> S = 1/2 ( 6/27 + 6/135 + 6/315 + 6/567 + 6/891 )

=> S = 1/2 ( 6/3.9 + 6/9.15 + 6/15.21 + 6/21.27 + 6/27.33 )

=> S = 1/2 ( 1/3 - 1/9 + 1/9 - 1/15 + ... + 1/27 - 1/33 )

=> S = 1/2 ( 1/3 - 1/33 )

=> S = 1/2 . 10/33

=> S = 5/33

\(S=\frac{1}{9}+\frac{1}{45}+\frac{1}{105}+\frac{1}{189}+\frac{1}{297}\)

\(S=\frac{1}{1.9}+\frac{1}{9.5}+\frac{1}{5.21}+\frac{1}{21.9}+\frac{1}{9.33}\)

\(5S=\frac{5}{1.9}+\frac{5}{9.5}+\frac{5}{5.21}+\frac{5}{21.9}+\frac{5}{9.33}\)

\(5S=1-\frac{1}{9}+\frac{1}{9}-\frac{1}{5}+\frac{1}{5}+\frac{1}{21}+\frac{1}{21}-\frac{1}{9}+\frac{1}{9}-\frac{1}{33}\)

\(5S=1-\frac{1}{33}\)

\(5S=\frac{32}{33}\)

\(S=\frac{32}{33}:5\)

\(S=\frac{32}{165}\)

Trả lời

B=1/45+1/105+1/189+1/279

=651+279+189+105/29295

=1190/29295

Bạn xem kiểm tra lại kĩ giúp mk nha, vì mk hay làm sai lém, hihi !

S+..... 

là sao vậy ??

S = NHA

(-6).43+45.(-6)+12.(-6)=(-6).(43+45+12)=(-6).100=(-600)

5.(-18-105)-105.(18-5)=5.(-18)+5.(-105)-105.(-18)+105.5=5.(-18)-105.(-18)=(-18).100=(-1800)

TICK MIK NHÉ.MIK TRẢ LỜI NHAH NHỨT NÈK

(-6).43+45.(-6)+12.(-6)=-600

5.(-18-105)-105.(18-5)=-2480

a. (-6) . 43 + 45.(-6) + 12.(-6)

= (-6) . (43 + 45 + 12)

= (-6) . 100

= -600

b. 5.(18 - 105) - 105.(18 - 5)

= 5.18 - 5.105 - 105.18 + 105.5

= 5.18 - 105.18

= 18.(5 - 105)

= 18.(-100)

= -1800

 = (-6) . (43+45+12) = (-6) . 100 = (-600)

                           * Đổi: 1 giờ 45 phút = 1,75 giờ

                                     105 phút = 1,75 giờ

1 giờ 45 phút x 3 + 1,75 giờ x 6 + 105 phút

 = 1,75 giờ x 3 + 1,75 giờ x 6 + 1,75 giờ x 1

= 1,75 giờ x ( 3 + 6 + 1 )

= 1,75 giờ x 10

= 17,5 giờ