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Passes Through the Point of Intersection of the Lines X + Y = 3 and 2x − 3y = 1 and is Parallel to X − Y − 6 = 0, Find a and B.

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Question

If the straight line \[\frac{x}{a} + \frac{y}{b} = 1\] passes through the point of intersection of the lines x + y = 3 and 2x − 3y = 1 and is parallel to x − y − 6 = 0, find a and b.

Answer in Brief
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Solution

The given lines are x + y = 3 and 2x − 3y = 1.
x + y − 3 = 0       ... (1)
2x − 3y − 1 = 0    ... (2)
Solving (1) and (2) using cross-multiplication method:

\[\frac{x}{- 1 - 9} = \frac{y}{- 6 + 1} = \frac{1}{- 3 - 2}\]

\[ \Rightarrow x = 2, y = 1\]

Thus, the point of intersection of the given lines is (2, 1).
It is given that the line \[\frac{x}{a} + \frac{y}{b} = 1\] passes through (2, 1).

\[\therefore \frac{2}{a} + \frac{1}{b} = 1\]    ... (3)

It is also given that the line \[\frac{x}{a} + \frac{y}{b} = 1\]  is parallel to the line x − y − 6 = 0.

Hence, Slope of \[\frac{x}{a} + \frac{y}{b} = 1\]

\[\Rightarrow y = - \frac{b}{a}x + b\]  is equal to the slope of x − y − 6 = 0 or, y = x − 6 

\[\therefore - \frac{b}{a} = 1\]

\[\Rightarrow b = - a\]            ... (4)

From (3) and (4): \[\frac{2}{a} - \frac{1}{a} = 1 \Rightarrow a = 1\]

From (4):
b = −1
∴ a = 1, b = −1

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Equations of Line in Different Forms - Equation of Family of Lines Passing Through the Point of Intersection of Two Lines
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Chapter 23: The straight lines - Exercise 23.10 [Page 78]

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R.D. Sharma Mathematics [English] Class 11
Chapter 23 The straight lines
Exercise 23.10 | Q 10 | Page 78

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