Question

$\left \{ {{x+y=8} \atop {x-y=1}} \right.$

$\left \{ {{3x+5y=21} \atop {2x-y=1}} \right.$

Ajutatima va rog...???

Answer 1

■Primul sistem: adunam cele doua relatii si observam ca y se reduce.Obtinem 2x=9=> x=4,5 si y= 8-4,5= 3,5 ■Al doilea sistem. din 2x-y= 1 scoatem pe y = 2x-1. Inlocuim in prima relatie si obtinem 3x+ 5(2x-1)=21 => 3x+ 10x- 5= 21 => 13x=21+5 => 13x= 26 => x=26/13=2. ● 2×2-1=y => 3=y

Answer 2

$a).\displaystyle \left \{ {{x+y=8} \atop {x-y=1}} \right. \\ 2x/=9 \\ x= \frac{9}{2} \\ \frac{9}{2} +y=8 \\ 9+2y=16 \\ 2y=16-9 \\ 2y=7 \\ y= \frac{7}{2}$

$\displaystyle b). \left \{ {{3x+5y=21} \atop {2x-y=1|\cdot 5}} \right. \\ \left \{ {{3x+5y=21} \atop {10x-5y=5}} \right. \\ 13x/=26 \\ x= \frac{26}{13} \\ x=2 \\ 3 \cdot 2+5y=21 \\ 6+5y=21 \\ 5y=21-6 \\ 5y=15 \\ y= \frac{15}{5} \\ y=3$