(c) (a) x2 - x = 0 ⇒ x(x- 1) = 0 ⇒ x - 0 and x = 1, This represent a pair of lines. (b) xy - x = 0 ⇒ x (y - 1) = 0 ⇒ x = 0, y = 1, This represent a pair of lines. (c ) y2 - x + 1 = 0 ⇒ y2 = ( x - 1 ) . This represent a parabola. Which does not represent a pair of lines (d) xy + x + y + 1 = 0⇒ x(y +1) + (y +1) = 0 ⇒ (y +1)(x + 1) = 0 ⇒ y = - 1 and x = 1 This represent a pair of lines