a)
\(x-\dfrac{3}{4}=\dfrac{1}{2}\\ x=\dfrac{1}{2}+\dfrac{3}{4}=\dfrac{5}{4}\)
b) \(\dfrac{3}{4}:x=\dfrac{1}{2}\)
\(x=\dfrac{3}{4}:\dfrac{1}{2}=\dfrac{3}{2}\)
c)
\(\left(3-x\right)\cdot\left(x+\dfrac{4}{5}\right)=0\\ \Rightarrow\left[{}\begin{matrix}3-x=0\\x+\dfrac{4}{5}=0\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=3-0=3\\x=0-\dfrac{4}{5}=-\dfrac{4}{5}\end{matrix}\right.\)
Vậy có 2 giá trị của \(x\) là \(3\) và \(-\dfrac{4}{5}\)