Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
\(\dfrac{2}{3}+\dfrac{1}{5}.\dfrac{10}{7}=\dfrac{2}{3}+\dfrac{10}{35}=\dfrac{70}{105}+\dfrac{30}{105}=\dfrac{100}{105}=\dfrac{50}{21}\)
a) Ta có: \(\dfrac{2}{3}+\dfrac{1}{5}\cdot\dfrac{10}{7}\)
\(=\dfrac{2}{3}+\dfrac{2}{7}\)
\(=\dfrac{14}{21}+\dfrac{6}{21}\)
\(=\dfrac{20}{21}\)
-6/8=-3/2
2/7
Quy đồng được 12/20+-35/20=-23/20
Quy đồng được -10/15+3/15=-7/15
Quy đồng lên được -4/26+-5/26=-9/26
Quy đồng lên được: -12/21+7/21=-5/21 nhé
\(\dfrac{-1}{8}+\dfrac{-5}{8}=\dfrac{-6}{8}=\dfrac{-3}{4}\)
\(\dfrac{-3}{7}+\dfrac{5}{7}=\dfrac{2}{7}\)
\(\dfrac{3}{5}+\dfrac{-7}{4}=\dfrac{12}{20}+\dfrac{-35}{20}=\dfrac{-23}{20}\)
\(\dfrac{-2}{3}+\dfrac{1}{5}=\dfrac{-10}{15}+\dfrac{3}{15}=\dfrac{-13}{15}\)
\(\dfrac{2}{13}+\dfrac{-5}{26}=\dfrac{-4}{26}+\dfrac{-5}{26}=\dfrac{-9}{26}\)
\(\dfrac{-4}{7}+\dfrac{1}{3}=\dfrac{-12}{21}+\dfrac{7}{21}=\dfrac{-5}{21}\)
5.\(-\dfrac{3}{7}+\dfrac{5}{13}+\dfrac{-4}{12}=-\dfrac{103}{273}\)
b.\(-\dfrac{5}{21}+\dfrac{-2}{21}+\dfrac{8}{24}=\dfrac{-5-2}{21}+\dfrac{8}{24}=-\dfrac{7}{21}+\dfrac{8}{24}=-\dfrac{1}{3}+\dfrac{8}{24}=0\)
c.\(\dfrac{5}{13}+\dfrac{-5}{7}+\dfrac{-20}{41}+\dfrac{8}{13}+\dfrac{-21}{41}=\left(\dfrac{5}{13}+\dfrac{8}{13}\right)+\left(\dfrac{-20}{41}+\dfrac{-21}{41}\right)+-\dfrac{5}{7}=1-1-\dfrac{5}{7}=-\dfrac{5}{7}\)
a) \(\dfrac{6}{{13}}.\dfrac{8}{{7}}.\dfrac{{ - 26}}{3}.\dfrac{{ - 7}}{8}\)
\(\begin{array}{l} = \left( {\dfrac{6}{{13}}.\dfrac{{ - 26}}{3}} \right).\left( {\dfrac{8}{7}.\dfrac{{ - 7}}{8}} \right)\\ = \dfrac{{6.\left( { - 26} \right)}}{{13.3}}.\dfrac{{8.\left( { - 7} \right)}}{{7.8}}\\= (- 4).\left( { - 1} \right) = 4\end{array}\)
b) \(\dfrac{6}{5}.\dfrac{3}{{13}} - \dfrac{6}{5}.\dfrac{{16}}{{13}}\)
\(\begin{array}{l} = \dfrac{6}{5}.\left( {\dfrac{3}{{13}} - \dfrac{{16}}{{13}}} \right)\\ = \dfrac{6}{5}.\dfrac{{3 - 16}}{{13}}\\ = \dfrac{6}{5}.\dfrac{{-13}}{{13}}\\= \dfrac{6}{5}.\left( { - 1} \right)\\ = \dfrac{{ - 6}}{5}\end{array}\)
2:
a: 2/9-x=-5/9
=>x=2/9+5/9=7/9
b: x-7/13=1/2
=>x=1/2+7/13=27/26
câu a
\(\dfrac{7}{4}+\dfrac{3}{2}+\dfrac{-9}{16}\\ =\dfrac{28}{16}+\dfrac{24}{16}-\dfrac{9}{16}=\dfrac{43}{16}\)
câu b
\(-\dfrac{2}{7}+\dfrac{3}{5}+\dfrac{9}{7}+\dfrac{-18}{5}\\ =-\dfrac{10}{35}+\dfrac{21}{35}+\dfrac{45}{35}-\dfrac{126}{35}\\ =-\dfrac{70}{35}=-2\)
câu c
\(-\dfrac{5}{13}+\dfrac{11}{10}-\dfrac{-9}{10}+\dfrac{-8}{13}\\ =-\dfrac{5}{13}+\dfrac{11}{10}+\dfrac{9}{10}-\dfrac{8}{13}\\ =-\dfrac{50}{130}+\dfrac{143}{130}+\dfrac{117}{130}-\dfrac{80}{130}\\ =\dfrac{130}{130}=1\)
bài 2
câu a
\(\dfrac{2}{9}-x=-\dfrac{5}{9}\\ x=\dfrac{2}{9}-\dfrac{-5}{9}\\ x=\dfrac{7}{9}\)
câu b
\(x+\dfrac{-7}{13}=\dfrac{1}{2}\\ x=\dfrac{1}{2}-\dfrac{-7}{13}\\ x=\dfrac{13}{26}+\dfrac{14}{26}\\ x=\dfrac{17}{26}\)
-5/13 . 3/7 - 2/7 . 8/13 + 5/13 . 1/7
= 5/13 . ( -3/7 + 1/7 ) - 2/7 . 8/13
= 5/13 . -2/7 - 2/7 . 8/13
= 2/7 . ( -5/13 - 8/13 )
= 2/7 . -1
= -2/7