Question

19.$\

$$\begin{cases}2x + y = 7\\\\y = 3\\end{cases}$$

$point: (2, 3) yes / no20.$\

$$\begin{cases}y = -3x + 1\\\\x + y = -2\\end{cases}$$

$point: (1, -4) yes / no21.$\

$$\begin{cases}y = 5\\\\2x + y = 9\\end{cases}$$

$point: (2, 5) yes / no22.$\

$$\begin{cases}y = x - 1\\\\3x + y = 8\\end{cases}$$

$point: (2, 1) yes / no

Explanation:

Step1: Check (2,3) in system 19

Substitute $x=2, y=3$:
$2(2)+3=7
ightarrow 7=7$; $y=3$ matches.

Step2: Check (1,-4) in system 20

Substitute $x=1, y=-4$:
$-4=-3(1)+1
ightarrow -4=-2$ (false); $1+(-4)=-2
ightarrow -3=-2$ (false).

Step3: Check (2,5) in system 21

Substitute $x=2, y=5$:
$y=5$ matches; $2(2)+5=9
ightarrow 9=9$.

Step4: Check (2,1) in system 22

Substitute $x=2, y=1$:
$1=2-1
ightarrow 1=1$; $3(2)+1=8
ightarrow 7=8$ (false).

Answer:

1. YES
2. NO
3. YES
4. NO