Optellen geeft \(4x=-2\text{,}\) dus \(x=-\frac{1}{2}\text{.}\)

\(\begin{rcases}x+y=3 \\ x=-\frac{1}{2}\end{rcases}\begin{matrix}-\frac{1}{2}+y=3 \\ y=3\frac{1}{2}\end{matrix}\)

De oplossing is \((x, y)=(-\frac{1}{2}, 3\frac{1}{2})\text{.}\)

\(\begin{cases}2p-2q=5 \\ 6p-5q=1\end{cases}\) \(\begin{vmatrix}3 \\ 1\end{vmatrix}\) geeft \(\begin{cases}6p-6q=15 \\ 6p-5q=1\end{cases}\)

Aftrekken geeft \(-q=14\text{,}\) dus \(q=-14\text{.}\)

\(\begin{rcases}2p-2q=5 \\ q=-14\end{rcases}\begin{matrix}2p-2⋅-14=5 \\ 2p=-23 \\ p=-11\frac{1}{2}\end{matrix}\)

De oplossing is \((p, q)=(-11\frac{1}{2}, -14)\text{.}\)

\(\begin{cases}3x-5y=2 \\ 5x-6y=-6\end{cases}\) \(\begin{vmatrix}6 \\ 5\end{vmatrix}\) geeft \(\begin{cases}18x-30y=12 \\ 25x-30y=-30\end{cases}\)

Aftrekken geeft \(-7x=42\text{,}\) dus \(x=-6\text{.}\)

\(\begin{rcases}3x-5y=2 \\ x=-6\end{rcases}\begin{matrix}3⋅-6-5y=2 \\ -5y=20 \\ y=-4\end{matrix}\)

De oplossing is \((x, y)=(-6, -4)\text{.}\)