câu a
\(x-\dfrac{1}{2}=\dfrac{7}{13}\cdot\dfrac{13}{28}\\ x-\dfrac{1}{2}=\dfrac{1}{4}\\ x=\dfrac{1}{4}+\dfrac{1}{2}\\ x=\dfrac{3}{4}\)
câu b
\(x\div\dfrac{15}{11}=-\dfrac{3}{12}\div8\\ x\div\dfrac{15}{11}=\dfrac{-1}{32}\\ x=-\dfrac{1}{32}\cdot\dfrac{15}{11}\\ x=-\dfrac{15}{352}\)
câu c
\(\left(2x+\dfrac{3}{8}\right)\cdot\dfrac{7}{4}=-\dfrac{21}{32}\\ 2x+\dfrac{3}{8}=-\dfrac{21}{32}\div\dfrac{7}{4}\\ 2x+\dfrac{3}{8}=-\dfrac{3}{8}\\ 2x=-\dfrac{3}{4}\\ x=-\dfrac{3}{4}\div2\\ x=-\dfrac{3}{8}\)
câu d
\(x^2+\dfrac{9}{-25}=\dfrac{2}{5}\div\dfrac{5}{8}\\ x^2+\dfrac{-9}{25}=\dfrac{16}{25}\\ x^2=\dfrac{16}{25}-\dfrac{-9}{25}\\ x^2=1\\ \Rightarrow x=1\)
d) \(x^2+\dfrac{9}{-25}=\dfrac{2}{5}:\dfrac{5}{8}\)
\(x^2-\dfrac{9}{25}=\dfrac{16}{25}\)
\(x^2=\dfrac{16}{25}+\dfrac{9}{25}\)
\(x^2=1\)
\(\Rightarrow x=-1;x=1\)
Câu a, b, c bạn subjects giải đúng rồi. Sai câu d