a: \(\Leftrightarrow\dfrac{16}{x}=\dfrac{-4}{5}\)
hay x=-20
b: =>x+7=-10
hay x=-17
\(-\dfrac{28}{35}=\dfrac{16}{x}\Leftrightarrow-\dfrac{4}{5}=\dfrac{16}{x}\)
\(\Rightarrow-4x=5\cdot16\)
\(\Rightarrow-4x=80\)
\(\Rightarrow x=-20\)
\(\dfrac{x+7}{15}=-\dfrac{24}{36}\Leftrightarrow\)\(\dfrac{x+7}{15}=-\dfrac{2}{3}\)
\(\Rightarrow3\left(x+7\right)=-2\cdot15\)
\(x+7=-30\div3\)
x+7=-10
x=-10-7
x=-17