Pair Of Straight Lines Question 57
Question: If the sum of the slopes of the lines given by $ x^{2}-2cxy-7y^{2}=0 $ is four times their product, then c has the value
[AIEEE 2004]
Options:
A) - 2
B) - 1
C) 2
D) 1
Show Answer
Answer:
Correct Answer: C
Solution:
Given pair of lines is $ x^{2}-2cxy-7y^{2}=0 $ Given, $ m_1+m_2=4m_1m_2\Rightarrow \frac{-2c}{7}=\frac{-4}{7}\Rightarrow c=2 $
$ [ \because \ m_1+m_2=-\frac{2h}{b}=\frac{-2c}{7};\ m_1m_2=\frac{-1}{7} ] $
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