Question

Solve the Equation
-6x-4y=21
-6x+3y=0

Answer 1

`\large\boxed{x=-(3)/(2),\ y=-3\to\left(-(3)/(2),\ -3\right)}`

Explanation:

`\left\{\begin{array}{ccc}-6x-4y=21\\-6x+3y=0&\text{change the signs}\end{array}\right\\\underline{+\left\{\begin{array}{ccc}-6x-4y=21\\6x-3y=0\end{array}\right}\qquad\text{add both sides of the equations}\\.\qquad-7y=21\qquad\text{divide both sides by (-7)}\\.\qquad\boxed{y=-3}\\\\\text{Put the value of}\ y\ \text{to the second equation}\ 6x-3y=0:\\\\6x-3(-3)=0\\6x+9=0\qquad\text{subtract 9 from both sides}\\6x=-9\qquad\text{divide both sides by 6}\\x=-(9:3)/(6:3)\\\boxed{x=-(3)/(2)}`