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Question

The graphs of the equations

\(4x + \frac{1}{3}y = \frac{8}{3}\) and \(\frac{1}{2}x + \frac{3}{4}y + \frac{5}{2} = 0\)  intersect at a point P. The point P also lies on the graph of the equation:

This question was previously asked in
SSC CGL 2020 Tier-II (English) Previous Year Paper (29-Jan-2022)
The correct answer is

3x – y – 7 = 0

Finding the Intersection Point of Linear Equations

The problem asks us to find the point where two given linear equations intersect and then determine which of the provided options represents an equation whose graph also passes through this intersection point. The intersection point of two graphs is the coordinate pair \((x, y)\) that satisfies both equations simultaneously.

The two given equations are:

  1. \(4x + \frac{1}{3}y = \frac{8}{3}\)
  2. \(\frac{1}{2}x + \frac{3}{4}y + \frac{5}{2} = 0\)

Simplifying the Linear Equations

To make the equations easier to solve, let's clear the fractions from each equation.

  • For the first equation, multiply the entire equation by the least common multiple of the denominators (which is 3):
    \(3 \times (4x + \frac{1}{3}y) = 3 \times \frac{8}{3}\)
    \(12x + y = 8\) (Let's call this Equation 3)
  • For the second equation, multiply the entire equation by the least common multiple of the denominators (which is 4):
    \(4 \times (\frac{1}{2}x + \frac{3}{4}y + \frac{5}{2}) = 4 \times 0\)
    \(2x + 3y + 10 = 0\) (Let's call this Equation 4)

Now we have a simpler system of linear equations:

  1. \(12x + y = 8\)
  2. \(2x + 3y + 10 = 0\)

Solving the System to Find the Intersection Point P

We can use either the substitution method or the elimination method to find the point of intersection P\((x, y)\). Let's use the substitution method.

From Equation 3, we can easily express \(y\) in terms of \(x\):
\(y = 8 - 12x\)

Now substitute this expression for \(y\) into Equation 4:

\(2x + 3(8 - 12x) + 10 = 0\)

Distribute the 3:

\(2x + 24 - 36x + 10 = 0\)

Combine like terms:

\((2x - 36x) + (24 + 10) = 0\)
\(-34x + 34 = 0\)

Isolate the term with \(x\):

\(-34x = -34\)

Solve for \(x\):

\(x = \frac{-34}{-34}\)
\(x = 1\)

Now substitute the value of \(x\) back into the equation \(y = 8 - 12x\) to find the value of \(y\):

\(y = 8 - 12(1)\)
\(y = 8 - 12\)
\(y = -4\)

So, the intersection point P has coordinates \((1, -4)\).

Checking which Equation also Passes Through P

The problem states that point P also lies on the graph of one of the given equations in the options. This means that the coordinates of P, \((1, -4)\), must satisfy that equation. We will substitute \(x=1\) and \(y=-4\) into each option to find which one holds true (equals zero).

Option Equation Substitute x=1, y=-4 Result Does P lie on the graph?
\(x + 2y - 5 = 0\) \(1 + 2(-4) - 5\) \(1 - 8 - 5 = -12\) No
\(3x - y - 7 = 0\) \(3(1) - (-4) - 7\) \(3 + 4 - 7 = 7 - 7 = 0\) Yes
\(x - 3y - 12 = 0\) \(1 - 3(-4) - 12\) \(1 + 12 - 12 = 1\) No
\(4x - y + 7 = 0\) \(4(1) - (-4) + 7\) \(4 + 4 + 7 = 15\) No

The substitution shows that only the second option, \(3x - y - 7 = 0\), is satisfied by the point \((1, -4)\).

Therefore, the point P\((1, -4)\) also lies on the graph of the equation \(3x - y - 7 = 0\).

Revision Table: Key Steps to Find the Intersection Point

Step Description Detail
1 Identify the System Note the two linear equations given.
2 Simplify Equations Clear fractions or decimals by multiplying by the LCM of denominators.
3 Solve the System Use substitution or elimination to find \(x\) and \(y\).
4 Find Point P The solution \((x, y)\) is the intersection point P.
5 Test Options Substitute the coordinates of P into each option equation.
6 Verify The equation that results in 0 is the correct one.

Additional Information on Linear Equations and Intersection Points

A linear equation in two variables, like \(Ax + By + C = 0\), represents a straight line when graphed on a coordinate plane. The intersection point of two lines is the single point that lies on both lines simultaneously. It is the unique solution \((x, y)\) that satisfies both equations in the system.

If two lines are parallel and distinct, they have no intersection point, and the system of equations has no solution. If two lines are identical (coincident), they intersect at every point, and the system has infinitely many solutions.

The method used here, solving the system of equations, is a standard algebraic approach to find the intersection point of lines. Another way is to graph both lines and visually identify the point of intersection, but this can be less precise.

Checking if a point lies on a line involves substituting the point's coordinates into the equation of the line. If the equation holds true (both sides are equal), the point is on the line; otherwise, it is not.

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Similar Questions

  1. The graphs of the linear equations 4x - 2y = 10 and 4x + ky = 2 intersect at a point (a, 4). The value of k is equal to:

  2. The area (in sq. units) of the triangle formed by the graphs of 8x + 3y = 24, 2x + 8 = y and the x-axis is:

  3. For what value of m will the system of equations 18x - 72y + 13 = 0 and 7x - my - 17 = 0 have no solution?

  4. What is the equation of the line perpendicular to the line 2x + 3y = -6 and having Y-intercept 3?

  5. What is the area (in unit squares) of the triangle enclosed by the graphs of 2x + 5y = 12, x + y = 3 and the x-axis?

  6. The graphs of the equations 3x - 20y - 2 = 0 and 11x - 5y + 61 = 0 intersect at P(a, b). What is the value of (a 2+ b 2- ab)/(a 2- b 2+ ab)?

  7. What is the area (in sq. units) of the triangle formed by the graphs of the equations 2x + 5y - 12 = 0, x + y = 3 and y = 0?

  8. What is the reflection of the point (5, -3) in the line y = 3?

  9. What is the area (in unit squares) of the region enclosed by the graphs of the equations

    2x – 3y + 6 = 0, 4x + y = 16 and y = 0?

  10. What is the reflection of the point (6, -1) in the line y = 2?


Important Questions from Co-ordinate Geometry

  1. The graphs of the linear equations 4x - 2y = 10 and 4x + ky = 2 intersect at a point (a, 4). The value of k is equal to:

  2. In which ratio the point (-3, p) divides the line segment joining the points (-5, -4) and (-2, 3)?

  3. The area (in sq. units) of the triangle formed by the graphs of 8x + 3y = 24, 2x + 8 = y and the x-axis is:

  4. In which quadrant both abscissa and ordinate are negative?

  5. Find the slope of the line joining the points (3, -4) and (5, 2).

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