Dijawab yah nomor 15 dan 25 Dan caranya yah

25).
y=2x+3
y=-2x-9
———  +
2y= -6
y= -3

y=2x+3
-3=2x+3
-6=2x
x=-3

tipot P(-3,-3), Q(1,9)
(y-y1)/(y2-y1)=(x-x1)/(x2-x1)
(y-9)/(9-(-3))=(x-1)/(1-(-3))
(y-9)/12=(x-1)/4   (di kali 4)
(y-9)/3=x-1
y-9=3x-3
y=3x+6
y=3(x+2) …..(D)

15).
a=-3, b=3
ax+by=ab
-3x+3y=(-3)(3)
-3x+3y=-9 …. (semua dibagi -3)
x-y=3

jwb : B. {(x,y}|x-y=3,x,y∈R}