Tìm x biết:     a) x + 1,05 = 4,25 - 0,2; b) 3/4- x = 1/2

a) \[x + 1,05 = 4,25 - 0,2\]

\[x + 1,05 = 4,05\]

\[x = 4,05 - 1,05\]

\[x = 3\].

Vậy \[x = 3\].

b) \(\frac{3}{4} - x = \frac{1}{2}\)

\[x = \frac{3}{4} - \frac{1}{2}\]

\(x = \frac{1}{4}\)

Vậy \(x = \frac{1}{4}\).

c) \(\left( {3x - 1} \right)\left( { - \frac{1}{2}x + 5} \right) = 0\)

Suy ra \(3x - 1 = 0\) hoặc \( - \frac{1}{2}x + 5 = 0\)

Trường hợp 1:

\(3x - 1 = 0\)

\(3x = 1\)

\(x = \frac{1}{3}\).

Vậy \(x \in \left\{ {\frac{1}{3};10} \right\}\).

Trường hợp 2:

\( - \frac{1}{2}x + 5 = 0\)

\( - \frac{1}{2}x =  - 5\)

\(x =  - 5:\left( {\frac{{ - 1}}{2}} \right)\)

\(x = 10\).