[tex] \left\{\begin{array}{ccc}-2x-7y=30&|\cdot7\\7x+4y=18&|\cdot2\end{array}\right\\\underline{+\left\{\begin{array}{ccc}-14x-49y=210\\14x+8y=36\end{array}\right}\ |\text{add both sides of the equations}\\.\ \ \ \ -41y=246\ \ \ |:(-41)\\.\ \ \ \ \ \ \ \ \ \ y=-6\\\\\text{substitute the value of y to the second equation}\\\\7x+4\cdot(-6)=18\\\\7x-24=18\ \ \ |+24\\\\7x=42\ \ \ |:7\\\\x=6\\\\Answer:\ x=6;\ y=-6\to(6;\ -6) [/tex]
