Question

Решите по действиям:
1)(-3,9×2,8+26,6)×(-3,2)-2,1
2)-5/9×0,87+(-5/9)×1,83
__________
Решите уравнение:
1)-0,25Х+0,8=1,3
2)(5-Х)(2Х+8)=0
3)-1,6/Х-2=2,8/4,2

Answer 1

▪1)
$( - 3.9 \times 2.8 + 26.6) \times ( - 3.2) - 2.1 = - 52.276\\ 1) \: \: \: - 3.9 \times 2.8 = - 10.92 \\ 2) \: \: \: - 10.92 + 26.6 = 15.68 \\ 3) \: \: \: 15.68 \times ( - 3.2) = - 50.176 \\ 4) \: \: \: - 50.176 - 2.1 = - 52.276$
▪2)
$- \frac{5}{9} \times 0.87 + ( - \frac{5}{9} ) \times 1.83 = - \frac{5}{9} \times (0.87 + 1.83) = - \frac{5}{9} \times 2.7 = - \frac{5 \times 27}{9 \times 10} = - \frac{3}{2} = - 1 \frac{1}{2} = - 1.5$
уравнения
▪1)
$- 0.25x + 0.8 = 1.3 \\ - 0.25x = 1.3 - 0.8 \\ - 0.25x = 0.5 \\ x = 0.5 \div ( - 0.25) = \frac{5}{10} \div ( - \frac{25}{100} ) = \frac{1}{2} \div ( - \frac{1}{4} ) = - \frac{4}{2} = - 2 \\ x = - 2$
▪2)
$(5 - x)(2x + 8) = 0 \\ 5 - x = 0 \\ x1 = 5 \\ - - - - - - - - \\ 2x + 8 = 0 \\ 2x = - 8 \\ x2 = - \frac{8}{2} \\ x2 = - 4 \\ - - - - - - - -$
▪3)
$\frac{ - 1.6}{x - 2} = \frac{2.8}{4.2} \\ 2.8x - 5.6 = - 6.72 \\ 2.8x = - 6.72 + 5.6 \\ 2.8x = - 1.12 \\ x = - 1.12 \div 2.8 = - \frac{112}{100} \times \frac{10}{28} = - \frac{4}{10} \\ x = - 0.4$