Question

помогите пожалуйста​

Answer 1

$1)\ \ 3x+y=4\ \ \to \ \ y=4-3x\\\\5x-y=2\ \ \to \ \ y=5x-2\\\\0,5y-x=7\ \ \to \ \ 0,5y=x+7\ \ ,\ \ y=\dfrac{x}{2}+\dfrac{7}{2}\ \ ,\ \ y=0,5x+3,5\\\\2x+\dfrac{1}{3}\, y-1=0\ \ \to \ \ \ \dfrac{1}{3}\, y=1-2x\ \ ,\ \ y=3-6x$

$2)\ \ 5x+2=0\ \ \to \ \ 5x=-2\ \ ,\ \ x=-\dfrac{2}{5}\ \ ,\ \ x=-0,4\\\\4x-3=0\ \ \to\ \ 4x=3\ \ ,\ \ x=\dfrac{3}{4}\ \ ,\ \ x=0,75\\\\2-3x=0\ \ \to \ \ 3x=2\ \ ,\ \ x=\dfrac{2}{3}\\\\\dfrac{1}{3}\, x+4=0\ \ \to \ \ \ \dfrac{1}{3}\, x=-4\ \ ,\ \ x=-12$

$3)\ \ \left\{\begin{array}{l}4x-3y=7\\2x+y=1\end{array}\right\\\\\\(-1;1):\ \ \left\{\begin{array}{l}-4-3=-7\ne 7\\-2+1=-1\ne 1\end{array}\right\\\\\\(1;-1):\ \ \left\{\begin{array}{l}4+3=7\ \ verno\\2-1=1\ \ verno\end{array}\right$

Решение системы - пара  ( 1 ; -1 ) .