Question

Решите 1,2,3 пожалуйста и побыстрее

Answer 1

1.
$2+7x=9x-7\\ 7x-9x=-7-2\\ -2x=-9\\ x=4.5$
3.
$\frac{1}{8} - \frac{3}{8} x= \frac{5}{8}x- \frac{7}{8} \\ - \frac{3}{8} x- \frac{5}{8}x=- \frac{7}{8} - \frac{1}{8} \\ -x=-1\\x=1$
4.
$- \frac{2}{3} a+ \frac{5}{7} = \frac{4}{21}+ \frac{5}{8} a\\ - \frac{2}{3} a - \frac{5}{8} a =- \frac{5}{7} + \frac{4}{21} \\ \frac{-16-15}{24} a = \frac{-15+4}{21} \\ \frac{-31}{24} a = \frac{-11}{21} \\ a = \frac{11}{21}* \frac{24}{31} = \frac{11*8}{7*31} = \frac{88}{217}$