Algebramedium · Past Paper
Two lines a1x + b1y = c1 and a2x + b2y = c2 are parallel if:
Aa1/a2 = b1/b2 != c1/c2
Ba1/a2 != b1/b2
Ca1/a2 = b1/b2 = c1/c2
Da1a2 + b1b2 = 0
✓ Correct Answer: A — a1/a2 = b1/b2 != c1/c2
Parallel lines have same slopes but different intercepts.
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