Boa noite

reta r

A(1/2, 0) , B(0,-1)

a/2 + b = 0
b = -1
a/2 - 1 = 0
a = -2

y = -2x - 1

reta s C(2, 0)

y = -2x + k = 0 
0 = -4 + k
k = 4
y = -2x + 4

reta t D(3,0)

y = -2x + k 
0 = -6 + k
k = 6

y = -2x + 6