Question:

The perpendicular from the origin to the line  \(y = mx + c\)  meets it at the point \((-1, 2)\). Find the values of m and c.

Updated On: Oct 22, 2023
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Solution and Explanation

The given equation of line is  \(y = mx + c.\)
It is given that the perpendicular from the origin meets the given line at \((-1, 2). \)
Therefore, the line joining the points\( (0, 0)\) and \((-1, 2)\) is perpendicular to the given line.

∴ Slope of the line joining\( (0, 0)\) and \((-1, 2)=\frac{2}{-1}=-2\)
The slope of the given line is m.

\(∴ m\times-2=-1\)       [The two lines are perpendicular]

\(⇒m=\frac{1}{2}\)
Since point \( (-1, 2)\) lies on the given line, it satisfies the equation \(y = mx + c.\)
\(∴ 2=m(-1)+c\)

\(⇒ 2=\frac{1}{2}(-1)+c\)

\(⇒ c = 2+\frac{1}{2} =\frac{ 5}{2}\)

Thus, the respective values of m and c are \(\frac{1}{2}\) and \(\frac{5}{2}\), respectively.

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Concepts Used:

Straight lines

A straight line is a line having the shortest distance between two points. 

A straight line can be represented as an equation in various forms,  as show in the image below:

 

The following are the many forms of the equation of the line that are presented in straight line-

1. Slope – Point Form

Assume P0(x0, y0) is a fixed point on a non-vertical line L with m as its slope. If P (x, y) is an arbitrary point on L, then the point (x, y) lies on the line with slope m through the fixed point (x0, y0) if and only if its coordinates fulfil the equation below.

y – y0 = m (x – x0)

2. Two – Point Form

Let's look at the line. L crosses between two places. P1(x1, y1) and P2(x2, y2)  are general points on L, while P (x, y) is a general point on L. As a result, the three points P1, P2, and P are collinear, and it becomes

The slope of P2P = The slope of P1P2 , i.e.

\(\frac{y-y_1}{x-x_1} = \frac{y_2-y_1}{x_2-x_1}\)

Hence, the equation becomes:

y - y1 =\( \frac{y_2-y_1}{x_2-x_1} (x-x1)\)

3. Slope-Intercept Form

Assume that a line L with slope m intersects the y-axis at a distance c from the origin, and that the distance c is referred to as the line L's y-intercept. As a result, the coordinates of the spot on the y-axis where the line intersects are (0, c). As a result, the slope of the line L is m, and it passes through a fixed point (0, c). The equation of the line L thus obtained from the slope – point form is given by

y – c =m( x - 0 )

As a result, the point (x, y) on the line with slope m and y-intercept c lies on the line, if and only if

y = m x +c