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Find k, if one of the lines given by 6x2 + kxy + y2 = 0 is 2x + y = 0.

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Question

Find k, if one of the lines given by 6x2 + kxy + y2 = 0 is 2x + y = 0.

Sum
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Solution

The auxiliary equation of the lines represented by 6x2 + kxy + y2 = 0 is m2 + km + 6 = 0

Since one of the line is 2x + y = 0 whose slope is m = - 2.

∴ m = - 2 is the root of the auxiliary equation m2 + km + 6 = 0.

∴ (-2)2 + k(-2) + 6 = 0

∴ 4 - 2k + 6 = 0

∴ 2k = 10

∴ k = 5 

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Chapter 4: Pair of Straight Lines - Miscellaneous Exercise 4 [Page 131]

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Balbharati Mathematics and Statistics 1 (Arts and Science) [English] Standard 12 Maharashtra State Board
Chapter 4 Pair of Straight Lines
Miscellaneous Exercise 4 | Q 5.7 | Page 131

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