NCERT Solutions
Class 11 - Mathematics - Chapter 9: STRAIGHT LINES
EXERCISE 9.1

Question. 1

Draw a quadrilateral in the Cartesian plane, whose vertices are \((-4,5), (0,7), (5,-5), (-4,-2)\). Also, find its area.

Answer:

\(\dfrac{121}{2}\) square unit.

Question. 2

The base of an equilateral triangle with side \(2a\) lies along the y-axis such that the mid-point of the base is at the origin. Find vertices of the triangle.

Answer:

(0, a), (0, -a) and \((-\sqrt{3} a, 0)\) or (0, a), (0, -a), and \((\sqrt{3} a, 0)\)

Question. 3

Find the distance between P \((x_1, y_1)\) and Q \((x_2, y_2)\) when (i) PQ is parallel to the y-axis, (ii) PQ is parallel to the x-axis.

Answer:

(i) \(|y_2 - y_1|\), (ii) \(|x_2 - x_1|\)

Question. 4

Find a point on the x-axis which is equidistant from the points (7, 6) and (3, 4).

Answer:

\(\left(\dfrac{15}{2}, 0\right)\)

Question. 5

Find the slope of a line which passes through the origin, and the mid-point of the line segment joining the points P (0, −4) and B (8, 0).

Answer:

\(-\dfrac{1}{2}\)

Question. 6

Without using the Pythagoras theorem, show that the points (4, 4), (3, 5) and (−1, −1) are the vertices of a right-angled triangle.

Question. 7

Find the slope of the line which makes an angle of \(30^\circ\) with the positive direction of y-axis measured anticlockwise.

Answer:

\(-\sqrt{3}\)

Question. 8

Without using distance formula, show that points (−2, −1), (4, 0), (3, 3) and (−3, 2) are the vertices of a parallelogram.

Question. 9

Find the angle between the x-axis and the line joining the points (3, −1) and (4, −2).

Answer:

135°

Question. 10

The slope of a line is double the slope of another line. If tangent of the angle between them is \(\dfrac{1}{3}\), find the slopes of the lines.

Answer:

1 and 2, or \(\dfrac{1}{2}\) and 1, or −1 and −2, or −\(\dfrac{1}{2}\) and −1

Question. 11

A line passes through \((x_1, y_1)\) and \((h, k)\). If slope of the line is m, show that \(k - y_1 = m(h - x_1)\).

NCERT Solutions Class 11 – Mathematics – Chapter 9: STRAIGHT LINES – EXERCISE 9.1 | Detailed Answers