Question

¼(1,6а-6,4)-⅖(2,5а-4,5) при а=-5​

Answer 1

Решение:

a= -5​

1/4(1,6a-6,4)-2/5(2,5a-4,5)=

$\frac{1}{4}(1,6a-6,4)-\frac{2}{5}(2,5a-4,5)= \frac{1}{4}(1,6*(-5)-6,4)-\frac{2}{5}(2,5*(-5)-4,5)= \\\\=\frac{1}{4}(-8-6,4)-\frac{2}{5}(-12,5-4,5)=\frac{1}{4}(-14,4)-\frac{2}{5}(-17)=\frac{1}{4}(-\frac{144}{10} )+\frac{2}{5}*17=\\\\=\frac{1}{4}*(-\frac{72}{5} )+\frac{34}{5}=-\frac{1}{4}*\frac{72}{5} +\frac{34}{5}=-1*\frac{18}{5} +\frac{34}{5}=-\frac{18}{5} +\frac{34}{5}=\frac{-18+34}{5} =\frac{16}{5}=3\frac{1}{5} .$

Ответ можно записать как:   $\frac{16}{5}$   или  $3\frac{1}{5}$   или  $3,2.$