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If the line 4x - 5y = 0 coincides with one of the lines given by ax2 + 2hxy + by2 = 0, then show that 25a + 40h + 16b = 0

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Question

If the line 4x - 5y = 0 coincides with one of the lines given by ax2 + 2hxy + by2 = 0, then show that 25a + 40h + 16b = 0

Sum
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Solution

The auxiliary equation of the lines represented by ax2 + 2hxy + by2 = 0 is bm2 + 2hm + a = 0.

Given that 4x - 5y = 0 is one of the lines represented by ax2 + 2hxy + by2 = 0.

The slope of the line 4x - 5y = 0 is `(-4)/-5 = 4/5`

∴ m = `4/5` is a root of the auxiliary equation bm2 + 2hm + a = 0.

∴ `"b"(4/5)^2 + 2"h"(4/5) + "a" = 0`

∴ `"16b"/25 + "8h"/5 + "a" = 0`

∴ 16b + 40h + 25a = 0 i.e.

∴ 25a + 40h + 16b = 0

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Chapter 4: Pair of Straight Lines - Miscellaneous Exercise 4 [Page 132]

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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 12 | Page 132

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