Question

Даю 50 баллов помогите

Answer 1

$1)-9x=21-3(5x-7)\\\\-9x=21-15x+21\\\\-9x+15x=42\\\\6x=42\\\\x=7\\\\Otvet:\boxed{7}$

$2)(a-5)^{2}-10(3-a)=a^{2}-10a+25-30+10a=a^{2} -5\\\\a=\frac{5}{3}\Rightarrow a^{2}-5=(\frac{5}{3})^{2}-5=\frac{25}{9}-5=2\frac{7}{9}-5=-2\frac{2}{9}\\\\Otvet:\boxed{-2\frac{2}{9}}$