Question 1
List all the linear pairs and vertically opposite angles you observe in Fig. 5.3:


When two lines cross each other, they form different types of angles.
Step 1 — Identifying Linear Pairs
Linear pairs are two angles that are next to each other. They form a straight line together. The sum of their measures is always 180 degrees.
Let us look at the diagram. Line and line intersect. We can find pairs of angles that form a straight line.
- Angles and are next to each other on line . They form a straight line.
- Angles and are next to each other on line . They form a straight line.
- Angles and are next to each other on line . They form a straight line.
- Angles and are next to each other on line . They form a straight line.

Step 2 — Identifying Vertically Opposite Angles
Vertically opposite angles are formed when two lines cross. They are directly opposite each other. These angles are always equal in measure.
Let us look at the diagram again. Line and line cross each other. We can find angles that are opposite to each other.
- Angle is opposite to angle .
- Angle is opposite to angle .

Answer
Linear Pairs: and , and , and , and . Pairs of Vertically Opposite Angles: and , and .
More questions in FIO
List all the linear pairs and vertically opposite angles you observe in Fig. 5.3:
Draw some lines perpendicular to the lines given on the dot paper in Fig. 5.10.
In Fig. 5.11, mark the parallel lines using the notation given above (single arrow, double arrow etc.). Mark the angle between perpendicular lines with a square symbol.
(a) How did you spot the perpendicular lines?
(b) How did you spot the parallel lines?
In the dot paper following, draw different sets of parallel lines. The line segments can be of different lengths but should have dots as endpoints.
Using your sense of how parallel lines look, try to draw lines parallel to the line segments on this dot paper.
(a) Did you find it challenging to draw some of them? (b) Which ones? (c) How did you do it?
In Fig. 5.13, which line is parallel to line a — line b or line c? How do you decide this?
Can you draw a line parallel to , that goes through point A? How will you do it with the tools from your geometry box? Describe your method.
Find the angles marked below.
Find the angle represented by .
In the figures below, what angles do and stand for?
In Fig. 5.33, and . Find angles , ,
In Fig. 5.34, is parallel to CD and CD is parallel to EF. Also, EA is perpendicular to AB. If , find the values of and .
What is the measure of angle in Fig. 5.35?
[Hint: Draw lines parallel to LM and PQ through points N and O.]