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Answer:
(a) x - y + 1 = 0
Step-by-step explanation:
One way to address multiple-choice questions is to try the answers to see what works.
For the lower left point (1, 2), the answer choices shown give ...
x -y +1 = 1 -2 +1 = 0 . . . . . equation works
-x -y +1 = -1 -2 +1 = -2 . . . doesn't work
y -x +1 = 2 -1 +1 = 2 . . . . . doesn't work
The appropriate choice is ...
x - y + 1 = 0
