Tìm \[x\].

a) x : 2,2 = (28,7 – 13,5).2 ;

b) \[\left( {3\frac{3}{4}.x + 75\% } \right):\frac{2}{3} = - 1\];

c) 4x – (3 + 5x) = 14

Hướng dẫn giải:

a) x : 2,2 = (28,7 – 13,5).2

x : 2,2 = 15,2 . 2

x : 2,2 = 30,4

x = 30,4 . 2,2

x = 66,88

Vậy x = 66,88

b) \[\left( {3\frac{3}{4}.x + 75\% } \right):\frac{2}{3} = - 1\]

\[\left( {\frac{{15}}{4}.x + \frac{{75}}{{100}}} \right):\frac{2}{3} = - 1\]

\[\left( {\frac{{15}}{4}.x + \frac{3}{4}} \right):\frac{2}{3} = - 1\]

\[\frac{{15}}{4}.x + \frac{3}{4} = \left( { - 1} \right).\frac{3}{2}\]

\[\frac{{15}}{4}.x + \frac{3}{4} = \frac{{ - 3}}{2}\]

\[\frac{{15}}{4}.x = \frac{{ - 3}}{2} - \frac{3}{4}\]

\[\frac{{15}}{4}.x = \frac{{ - 6}}{4} - \frac{3}{4}\]

\[\frac{{15}}{4}.x = \frac{{ - 9}}{4}\]

\(x = \frac{{ - 9}}{4}:\frac{{15}}{4}\)

\(x = \frac{{ - 9}}{4}.\frac{4}{{15}}\)

\(x = \frac{{ - 3}}{5}\)

Vậy \(x = \frac{{ - 3}}{5}.\)

c) 4x – (3 + 5x) = 14       

4x – 3 – 5x = 14

4x – 5x = 14 + 3

– x = 17

x = –17

Vậy x = –17