Question

Solving linear combination

Answer 1

$\underline{+\left\{\begin{array}{ccc}4x+5y=16\\-4x-10y=4\end{array}\right}\qquad\text{add both sides of the equations}\\.\qquad\qquad-5y=20\qquad\text{divide both sides by (-5)}\\.\qquad\qquad\boxed{y=-4}\\\\\text{Put the value of y to the first equation:}\\\\4x+5(-4)=16\\4x-20=16\qquad\text{add 20 to both sides}\\4x=36\qquad\text{divide both sides by 4}\\\boxed{x=9}\\\\Answer:\ \boxed{x=9\ and\ y=-4\to(9,\ -4)}$