a)(1/4+3/4)-(5/13+8/13)+2/11=1-1+2/11=2/11

b)(21/31+10/31)-16/7+(44/53+9/53)=1+1-16/7=14/7-16/7=-2/7

bằng2/11

         -16/7

a, \(\left(\frac{1}{4}+\frac{-5}{13}\right)+\left(\frac{2}{11}+\frac{-8}{13}+\frac{3}{4}\right)\)

\(=\left(\frac{1}{4}-\frac{5}{13}\right)+\left(\frac{2}{11}-\frac{8}{13}+\frac{3}{4}\right)\)

\(=\frac{1}{4}-\frac{5}{13}+\frac{2}{11}-\frac{8}{13}+\frac{3}{4}=1-1+\frac{2}{11}=\frac{2}{11}\)( vì \(\left(\frac{1}{4}+\frac{3}{4}\right)+\left(-\frac{5}{13}-\frac{8}{13}+\frac{2}{11}\right)\))

b, \(\left(\frac{21}{31}+\frac{-16}{7}\right)+\left(\frac{44}{53}+\frac{10}{31}\right)+\frac{9}{53}\)

\(=\frac{21}{31}-\frac{16}{7}+\frac{44}{53}+\frac{10}{31}+\frac{9}{53}\)

\(=1-\frac{16}{7}+1=\frac{7}{7}-\frac{16}{7}+\frac{7}{7}=-\frac{2}{7}\)

a) \(\left(\frac{1}{4}+-\frac{5}{13}\right)+\left(\frac{2}{11}+-\frac{8}{13}+\frac{3}{4}\right)\)

\(=\frac{2}{11}+\left(\frac{1}{4}+\frac{3}{4}\right)+\left(-\frac{5}{13}+-\frac{8}{13}\right)\)

\(=\frac{2}{11}+1+\left(-1\right)\)

\(=\frac{2}{11}+0\)

\(=\frac{2}{11}\)

b) \(\left(\frac{21}{31}+-\frac{16}{7}\right)+\left(\frac{44}{53}+\frac{10}{31}\right)+\frac{9}{53}\)

\(=-\frac{16}{7}+\left(\frac{21}{31}+\frac{10}{31}\right)+\left(\frac{44}{53}+\frac{9}{53}\right)\)

\(=-\frac{16}{7}+1+1\)

\(=-\frac{16}{7}+2\)

=\(-\frac{2}{7}\)

c) \(\frac{\frac{9}{45}-\frac{4}{13}-\frac{1}{3}}{\frac{3}{13}-\frac{1}{15}+\frac{2}{3}}\)

\(=-\frac{43}{81}\)

\(a)\frac{-3}{4}+\frac{3}{7}+-\frac{1}{4}+\frac{4}{9}+\frac{4}{7}\)

\(=\left(\frac{-3}{4}+-\frac{1}{4}\right)+\left(\frac{3}{7}+\frac{4}{7}\right)+\frac{4}{9}\)

\(=-1+1+\frac{4}{9}\)

\(=\frac{4}{9}\)

\(\frac{-3}{4}+\frac{3}{7}+\frac{-1}{4}+\frac{4}{9}+\frac{4}{7}\)

\(=\left(\frac{-3}{4}+\frac{-1}{4}\right)+\left(\frac{3}{7}+\frac{4}{7}\right)+\frac{4}{9}\)

\(=\left(-1\right)+1+\frac{4}{9}\)

\(=0+\frac{4}{9}\)

\(=\frac{4}{9}\)

GIÚP MIK IK XIN CÁC BN ĐÓ

a, 1 - 7x = 3x - 4

=> -7x - 3x = - 4 - 1

=> - 10x = - 5

=> x = 1/2

vậy_

b, đặt  \(A=\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...+\frac{1}{3^{99}}\)

\(3A=1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^{98}}\)

\(3A-A=1-\frac{1}{3^{99}}\)

\(A=\frac{1-\frac{1}{3^{99}}}{2}\)

mk chỉ bt lm mấy phần hui à!

d)\(\frac{5}{17}+\frac{-4}{7}-\frac{20}{31}+\frac{12}{17}-\frac{11}{31}\)\(=\left(\frac{5}{17}+\frac{12}{17}\right)+\left(\frac{-20}{31}-\frac{11}{31}\right)+\frac{-4}{7}\)

\(=\frac{17}{17}+\frac{-31}{31}+\frac{-4}{7}\)\(=1+\left(-1\right)+\frac{-4}{7}\)\(=0+\frac{-4}{7}\)\(=-\frac{4}{7}\)

e)\(\frac{155-\frac{10}{7}-\frac{5}{11}+\frac{5}{23}}{403-\frac{20}{7}-\frac{13}{3}+\frac{13}{23}}\)

mk xl,mk ko bt lm các phần còn lại!

a) \(\frac{4}{9}\)( cái này gọp âm lại tính, gọp dương lại tính)

b)\(\frac{28}{9}\)

c)bài này gọp mẫu chung lại r tính