# Ex.7.2 Q3 Coordinate Geometry Solution - NCERT Maths Class 10

## Question

To conduct Sports Day activities, in your rectangular shaped school ground \(ABCD\), lines have been drawn with chalk powder at a distance of \(1\rm\,m \) each. \(100\) flower pots have been placed at a distance of \(1\rm\,m \) from each other along \(AD\), as shown in the following figure. Niharika runs \(\begin{align}\frac{1}{4}\end{align}\)th the distance \(AD\) on the \(2^\rm {nd}\) line and posts a green flag. Preet runs \(\begin{align}\frac{1}{5}\end{align}\)th the distance \(AD\) on the eighth line and posts a red flag. What is the distance between both the flags? If Rashmi has to post a blue flag exactly halfway between the line segments joining the two flags, where should she post her flag?

## Text Solution

**Reasoning:**

The coordinates of the point \(P(x, y)\) which divides the line segment joining the points \(A(x_1, y_1)\) and \(B(x_2, y_2)\), internally, in the ratio \(m_1 : m_2\) is given by the Section Formula.

**What is Known?**

- The school ground \(ABCD\) is rectangular shaped.
- Lines are drawn at a distance of \(1\rm\,m \) each and \(100\) flower pots have been placed at a distance of \(1\rm\,m \) each along \(AD\).
- The distance covered by Niharika and Preet on line \(AD\).

**What is Unknown?**

- The distance between the flags posted by Niharika and Preet.
- The position on the line segment where Rashmi has to post the flag.

**Steps:**

From the Figure,

Given,

- By observation, that Niharika posted the green flag at of the distance \(P\) i.e., \(\begin{align}\left( {\frac{1}{4} \times 100} \right)m = 25\,m\end{align}\) from the starting point of \(2^\rm{nd}\) Therefore, the coordinates of this point \(P\) is \((2, 25)\).

- Similarly, Preet posted red flag at \(\frac{{1}}{5}\) of the distance \(Q\) i.e., \(\begin{align}\left( {\frac{1}{5} \times 100} \right)m = 20\,m\end{align}\) from the starting point of \(8^\rm {th}\) Therefore, the coordinates of this point \(Q\) are \((8, 20)\)

We know that the distance between the two points is given by the Distance Formula,

\[\begin{align}&\sqrt {{{\left( x_1 - x_2 \right)^2 + \left(y_1 - y_2 \right)}^2}} \;\;\dots(1)\end{align}\]

To find the distance between these flags \(PQ\) by substituting the values in Equation (1),

\(\begin{align}PQ &= \sqrt {{{(8 - 2)}^2} + {{(25 - 20)}^2}} \\ &= \sqrt {36 + 25} \\ &= \sqrt {61}\text{ m} \end{align}\)

- The point at which Rashmi should post her blue flag is the mid-point of the line joining these points.
- Let this point be \(M \;(x, y)\).

By Section formula

\[\begin{align} P(x,y)& \!=\! \left[ {\frac{{mx_2 \! + \! nx_1}}{{m \! + \! n}}\!,\!\frac{{my_2 \! + \! ny_1}}{{m \! + \! n}}} \!\right]\;\;\dots(2) \; \end{align}\]

\(\begin{align}x &= \frac{{2 + 8}}{2}, \qquad y = \frac{{25 + 20}}{2}\\x &= \frac{{10}}{2}, \qquad\quad\; y = \frac{{45}}{2}\\x &= 5, \qquad\qquad \;y = 22.5\end{align}\)

Therefore, Rashmi should post her blue flag at \(22.5\;\rm m\) on \(5^\rm {th}\) line