15. If the lines representing the pair of linear equations a1x + b1y + c1 = 0 and a2x + b2y + c2 = 0 are coincident, then

(a) a₁/a₂ = b₁/b₂
(b) a₁/a₂ = b₁/b₂ = c₁/c₂
(c) a₁/a₂ ≠ b₁/b₂
(d) a₁/a₂ = b₁/b₂ ≠ c₁/c₂
Answer: (b) a₁/a₂ = b₁/b₂ = c₁/c₂
If the lines representing the pair of linear equations a₁x + b₁y + c₁ = 0 and a₂x + b₂y + c₂ = 0 are coincident, then a₁/a₂ = b₁/b₂ = c₁/c₂.