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Question

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?

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

14

  • Question Analysis: The problem asks us to find the area of a specific region in the coordinate plane. This region is defined as the space enclosed by the graphs of three linear equations: $2x - 3y + 6 = 0$, $4x + y = 16$, and $y = 0$.
  • Keywords: Area, region enclosed, graphs, equations, $2x - 3y + 6 = 0$, $4x + y = 16$, $y = 0$.

Defining the Boundary Equations

To find the area of the enclosed region, we first need to clearly identify the lines that form its boundaries:

  • Line 1: $2x - 3y + 6 = 0$
  • Line 2: $4x + y = 16$
  • Line 3: $y = 0$. This equation represents the x-axis.

Calculating the Vertices of the Region

The region enclosed by these lines forms a polygon. The corners (vertices) of this region are found by determining where these lines intersect each other.

  1. Intersection of Line 1 ($2x - 3y + 6 = 0$) and Line 3 ($y = 0$): Substitute $y = 0$ into the first equation: $2x - 3(0) + 6 = 0$ $2x + 6 = 0$ $2x = -6$ $x = -3$ So, the first vertex is A = (-3, 0).
  2. Intersection of Line 2 ($4x + y = 16$) and Line 3 ($y = 0$): Substitute $y = 0$ into the second equation: $4x + 0 = 16$ $4x = 16$ $x = 4$ So, the second vertex is B = (4, 0).
  3. Intersection of Line 1 ($2x - 3y + 6 = 0$) and Line 2 ($4x + y = 16$): First, express $y$ from Line 2: $y = 16 - 4x$. Now, substitute this expression for $y$ into Line 1: $2x - 3(16 - 4x) + 6 = 0$ $2x - 48 + 12x + 6 = 0$ Combine like terms: $14x - 42 = 0$ $14x = 42$ $x = \frac{42}{14} = 3$ Now find the corresponding $y$ value using $y = 16 - 4x$: $y = 16 - 4(3)$ $y = 16 - 12$ $y = 4$ So, the third vertex is C = (3, 4).

The vertices of the enclosed region are (-3, 0), (4, 0), and (3, 4). These points form a triangle.

Determining the Area of the Triangle

The area of the enclosed region, which is a triangle with vertices A(-3, 0), B(4, 0), and C(3, 4), can be calculated using the base and height.

  • Base: The base of the triangle lies along the x-axis (where $y = 0$) between vertex A (-3, 0) and vertex B (4, 0). The length of the base is the distance between these two points: $\text{Base} = |4 - (-3)| = |4 + 3| = 7$ units.
  • Height: The height of the triangle is the perpendicular distance from the third vertex C (3, 4) to the base (the x-axis). This distance is simply the absolute value of the y-coordinate of vertex C. $\text{Height} = |4| = 4$ units.
  • Area Calculation: The formula for the area of a triangle is $\frac{1}{2} \times \text{base} \times \text{height}$. $\text{Area} = \frac{1}{2} \times 7 \times 4$ $\text{Area} = \frac{1}{2} \times 28$ $\text{Area} = 14$ unit squares.

Conclusion on the Region's Area

The calculated area of the region enclosed by the graphs of the equations $2x - 3y + 6 = 0$, $4x + y = 16$, and $y = 0$ is 14 unit squares.

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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:

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