Question

  1) 5x-2y=4.         2) 3x-5y=13  x-2y=53x+y=9

Answer 1

$\left\{\begin{array}{ccc}5x-2y=4\\3x+y=9&/\cdot2\end{array}\right\\+\left\{\begin{array}{ccc}5x-2y=4\\6x+2y=18\end{array}\right\\----------\\.\ \ \ \ \ 11x=22\ \ \ \ /:11\\.\ \ \ \ \ \ \ x=2\\\\3\cdot2+y=9\\6+y=9\\y=9-6\\y=3\\\\Answer:x=2;\ y=3$


$\left\{\begin{array}{ccc}3x-5y=13\\x-2y=5\end{array}\right\\\left\{\begin{array}{ccc}3x-5y=13\\x=2y+5\end{array}\right\\\\substitute:\\\\3(2y+5)-5y=13\\6y+15-5y=13\\y=13-15\\y=-2\\\\x=2\cdot(-2)+5=-4+5=1\\\\Answer:x=1;\ y=-2.$