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Question

A line passes through (2, 2) and is perpendicular to the line 3x + y = 3. Its y-intercept is

This question was previously asked in
NDA II 2015 GAT Previous Year Paper (16-Dec-2015)
The correct answer is

4/3

Understanding the Problem: Finding the Y-intercept of a Perpendicular Line

The question asks us to find the y-intercept of a specific line. We are given two key pieces of information about this line:

  • It passes through a known point, (2, 2).
  • It is perpendicular to another given line, 3x + y = 3.

To find the y-intercept, we first need to determine the equation of the required line. We can do this by finding its slope and using the given point.

Step-by-Step Solution

Step 1: Find the Slope of the Given Line

The given line has the equation \(3x + y = 3\). To find its slope, we can rewrite this equation in the slope-intercept form, which is \(y = mx + c\), where \(m\) is the slope and \(c\) is the y-intercept.

Rearranging the equation \(3x + y = 3\):

Subtract \(3x\) from both sides:

\(y = -3x + 3\)

Comparing this to \(y = mx + c\), we can see that the slope of the given line is \(m_1 = -3\).

Step 2: Find the Slope of the Required Line

We are told that the required line is perpendicular to the line \(3x + y = 3\). For two non-vertical lines to be perpendicular, the product of their slopes must be -1.

Let \(m_2\) be the slope of the required line. Then, we have:

\(m_1 \times m_2 = -1\)

Substituting the value of \(m_1\):

\(-3 \times m_2 = -1\)

To find \(m_2\), divide both sides by -3:

\(m_2 = \frac{-1}{-3} = \frac{1}{3}\)

So, the slope of the required line is \(\frac{1}{3}\).

Step 3: Find the Equation of the Required Line

We know the required line passes through the point \((x_1, y_1) = (2, 2)\) and has a slope \(m = \frac{1}{3}\). We can use the point-slope form of a linear equation, which is \(y - y_1 = m(x - x_1)\).

Substitute the known values into the point-slope form:

\(y - 2 = \frac{1}{3}(x - 2)\)

Now, we can simplify this equation to get it into slope-intercept form \(y = mx + c\):

\(y - 2 = \frac{1}{3}x - \frac{1}{3}(2)\)

\(y - 2 = \frac{1}{3}x - \frac{2}{3}\)

Add 2 to both sides of the equation:

\(y = \frac{1}{3}x - \frac{2}{3} + 2\)

To add \(- \frac{2}{3}\) and 2, we need a common denominator:

\(y = \frac{1}{3}x - \frac{2}{3} + \frac{6}{3}\)

\(y = \frac{1}{3}x + \frac{4}{3}\)

This is the equation of the required line in the form \(y = mx + c\).

Step 4: Determine the Y-intercept

In the slope-intercept form of a linear equation, \(y = mx + c\), the constant term \(c\) represents the y-intercept. The y-intercept is the point where the line crosses the y-axis, which occurs when \(x = 0\).

From the equation we found, \(y = \frac{1}{3}x + \frac{4}{3}\), the constant term is \(\frac{4}{3}\).

Alternatively, set \(x = 0\) in the equation:

\(y = \frac{1}{3}(0) + \frac{4}{3}\)

\(y = 0 + \frac{4}{3}\)

\(y = \frac{4}{3}\)

The y-intercept is \(\frac{4}{3}\).

Conclusion: Finding the Y-intercept

The y-intercept of the line that passes through (2, 2) and is perpendicular to the line \(3x + y = 3\) is \(\frac{4}{3}\). This corresponds to one of the given options.

Revision Table: Key Concepts for Finding Y-intercept

Concept Description Formula/Example
Slope-Intercept Form A way to write linear equations (\(y = mx + c\)) where \(m\) is the slope and \(c\) is the y-intercept. \(y = 2x + 5\) (Slope = 2, Y-intercept = 5)
Slope of a Line A measure of the steepness of a line (\(m = \frac{\Delta y}{\Delta x}\)). Line \(y = -3x + 3\) has slope \(m = -3\).
Perpendicular Lines Two lines that intersect at a 90-degree angle. Their slopes (\(m_1, m_2\)) have a product of -1 (\(m_1 m_2 = -1\)), provided neither line is vertical. If \(m_1 = 2\), then \(m_2 = -\frac{1}{2}\) for a perpendicular line.
Point-Slope Form A way to write linear equations using a point \((x_1, y_1)\) the line passes through and its slope \(m\). \(y - y_1 = m(x - x_1)\)
Y-intercept The point where the line crosses the y-axis. The x-coordinate is always 0. For \(y = \frac{1}{3}x + \frac{4}{3}\), the y-intercept is \(\frac{4}{3}\), occurring at the point \((0, \frac{4}{3})\).

Additional Information: Coordinate Geometry Basics

Coordinate geometry is a branch of mathematics that uses coordinates to study geometric shapes and figures. Understanding the relationships between lines, points, and slopes is fundamental.

  • Every point in a 2D plane can be represented by an ordered pair \((x, y)\).
  • A line is defined by an equation that the coordinates of all points on the line satisfy.
  • Parallel lines have the same slope.
  • Vertical lines have undefined slopes and equations of the form \(x = a\). Their y-intercept is undefined unless the line is the y-axis itself (\(x=0\)).
  • Horizontal lines have a slope of 0 and equations of the form \(y = b\). Their y-intercept is \(b\).

Finding the equation of a line is a common task in coordinate geometry. The method used depends on the information given (e.g., two points, a point and a slope, slope and y-intercept).

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Important Questions from Properties of Lines

  1. The slope of the line 4x + 3y - 4 = 0 is:

  2. Let x + 2y + 4 = 0 and -4x + 2y - 3 = 0 be the equations of two straight lines. Then

  3. If the slope of the line joining the points (k, 4) and (-3, -2) is \(\frac{1}{2}\), then the value of k is

  4. If the equation

    3x2 + 7xy + 2y2 + 5x + 5y + k = 0

    represents a pair of straight lines, then the value of k is

  5. If the sum of the slopes of the lines given by x2 - 2cxy - 7y2 = 0 is four time their products, then the value of c is

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