Question

The value of k for which the pair of equations 3x + 4y + 2 = 0 and 9x + 12y + k = 0 represent coincident lines is …………….. 

A) 2 

B) 3 

C) 6 

D) 12

Answer 1

Correct option is (C) 6

Condition for two line to be coincident lines is

\(\frac{a_1}{a_2}=\frac{b_1}{b_2}=\frac{c_1}{c_2}\)

\(\therefore\) \(\frac39=\frac4{12}=\frac2k\)

\(\Rightarrow\) \(\frac2k=\frac13\)

\(\Rightarrow\) \(k=2\times3=6\)

Answer 2

Correct option is C) 6