Condition to represent pair of lines circle and conic

Which of the following equations represents a pair of real and coincident straight lines?

Which of the following equations represents a pair of real and coincident straight lines?

Which of the following equation does not represent a pair of lines ?

Which of the following equation does not represent a pair of lines ?

Condition that a pair of lines are at right angle is

What is the General equation of second degree and condition for represent pair of lines?

The condition for the equation x^2(lambda+mu)xy+lambdamuy^2+x+muy=0 to represent pair of parallel lines and the distance between them are

Under what condition do > represent direction cosines of a line ?

Which of the following represents pair of lines?