\(a,\dfrac{15}{28}+\dfrac{-1}{4}=\dfrac{15}{28}+\dfrac{-7}{28}=\dfrac{8}{28}=\dfrac{2}{7}\\ b,\dfrac{2}{7}-\dfrac{-1}{4}=\dfrac{8}{28}-\dfrac{-7}{28}=\dfrac{15}{28}\)

\(c,\dfrac{-14}{3}:2=\dfrac{-14}{3}\times\dfrac{1}{2}=\dfrac{-7}{3}\\ d,\dfrac{-7}{15}.\dfrac{5}{8}.\dfrac{15}{-7}.\left(-16\right)=\left(\dfrac{-7}{15}.\dfrac{15}{-7}\right)\left[\dfrac{5}{8}.\left(-16\right)\right]=1.\left(-10\right)=-10\)

C

B

ko cần thì thôi

cô dở hơi, hết xinh r :V

đề bảo sắp xếp thôi mà

quy đồng lâu vl 

\(\dfrac{4a-b}{3a+3}+\dfrac{4b-a}{3b-3}\\ =\dfrac{4a-b}{3a+a-b}+\dfrac{4b-a}{3b-\left(a-b\right)}\\ =\dfrac{4a-b}{4a-b}+\dfrac{4b-a}{3b-a+b}\\ =1+\dfrac{4b-a}{4b-a}\\ =1+1\\ =2\)

Cô xinh phết :>

\(a,\dfrac{-2}{3};\dfrac{-3}{12};\dfrac{-1}{-6};\dfrac{3}{4}\\ c,\dfrac{3}{-4}-\dfrac{1}{2};0;\dfrac{3}{10};\dfrac{-2}{-5}\\ b,-1;\dfrac{-7}{9};\dfrac{-1}{3};0;\dfrac{-1}{-4};\dfrac{5}{12}\\ d,\dfrac{23}{-25};\dfrac{-7}{10};\dfrac{-2}{5}\dfrac{17}{-50}\dfrac{-37}{-150}\)