287. Упростите: a) -3 (0,2x + 0,4y) + (1,6x + 2,8y) 2; б)(4m-1,4)-(6m+ 2,7).

Ответ: a) 2.6x + 4.4y; б) (8m-2,8)-(6m+ 2,7)

a) \[-3(0.2x + 0.4y) + (1.6x + 2.8y) \cdot 2 = -0.6x - 1.2y + 3.2x + 5.6y = (-0.6x + 3.2x) + (-1.2y + 5.6y) = 2.6x + 4.4y\]

б) \frac{2}{7}(\frac{4}{3}m - 1.4) - \frac{2}{9}(6m + 2.7)\]

\[\frac{2}{7} \cdot \frac{4}{3}m - \frac{2}{7} \cdot 1.4 - \frac{2}{9} \cdot 6m - \frac{2}{9} \cdot 2.7\]

\[\frac{8}{21}m - \frac{2.8}{7} - \frac{12}{9}m - \frac{5.4}{9}\]

\[\frac{8}{21}m - 0.4 - \frac{4}{3}m - 0.6\]

\[(\frac{8}{21} - \frac{4}{3})m - 0.4 - 0.6\]

\[(\frac{8}{21} - \frac{28}{21})m - 1\]

\[-\frac{20}{21}m - 1\]

Ответ: a) 2.6x + 4.4y; б) (8m-2,8)-(6m+ 2,7)