3x - 4y = 7
7x + 8y = - 105
x = <img src="https://tex.z-dn.net/?f=%28%20%5Cfrac%7B7%2B4y%7D%7B3%7D%20%29" />
7<img src="https://tex.z-dn.net/?f=%28%20%5Cfrac%7B7%2B4y%7D%7B3%7D%20%29" /> + 8y = - 105
<img src="https://tex.z-dn.net/?f=%20%5Cfrac%7B49%2B28y%7D%7B3%7D%20%2B%20%5Cfrac%7B24y%7D%7B3%7D%20%3D%20%5Cfrac%7B-315%7D%7B3%7D%20" />
28y + 24y = - 315 - 49
52y = - 364
y = - 364 / 52
y = - 7
x = <img src="https://tex.z-dn.net/?f=%28%20%5Cfrac%7B7%2B4%28-7%29%7D%7B3%7D%20%29" />
x = <img src="https://tex.z-dn.net/?f=%28%20%5Cfrac%7B-21%7D%7B3%7D%20%29" />
x = - 7
Solución :
los valores - 7, - 5 no son la solución del sistema.