Question

Which of the following second degree equation represented a pair of straight lines

• A. $x^{2} - xy - y^{2} = 1$
• B. $- x^{2} + xy - y^{2} = 1$
• C. $4x^{2} - 4xy + y^{2} = 4$
• D. $x^{2} + y^{2} = 4$

Answer 1

Answer: (C)

$4x^{2} - 4xy + y^{2} = 4$

Answer 2

We have to check for each equation separately.

Option (4) cannot be because it is a circle.

Considering option (1) $\Delta \neq 0,\mspace{6mu}$ option (2) $\Delta \neq 0$and for option (3) $\Delta = 0$.