Opgave 1

$\cases{2x+3y=12\cr₃x+7y=8}$

$\cases{6x+9y=36\cr₆x+14y=16}$

Trek (1) van (2) af:

$5y=-20$

$\cases{y=-4\cr x=12}$

Opgave 2

$\cases{2x+3y=12\cr y=2x+4}$

$\cases{2x+3(2x+4)=12\cr y=2x+4}$

$\cases{2x+6x+12=12\cr y=2x+4}$

$\cases{8x=0\cr y=2x+4}$

$\cases{x=0\cr y=4}$

Opgave 3

$\cases{y=x²-4x\cr y=2x-4}$

$x²-4x=2x-4$
$x²-6x+4=0$
$(x-3)²-9+4=0$
$(x-3)²-5=0$
$(x-3)²=5$
$x-3=-\sqrt 5\vee x-3=\sqrt 5$
$x=3-\sqrt 5\vee x=3+\sqrt 5$

$\cases{x=3-\sqrt 5\cr y=2-2\sqrt 5}\vee \cases{x=3+\sqrt 5\cr y=2+2\sqrt 5}$